These are the installation instructions for my PHPBB Pingback / Trackback modification.

Required items:
phpBB (which obviously requires a web server, a database, and PHP)
phpBB_Fetch_All
phpBB pbtb base files

NOTE: I have only tested this with phpBB 2.0.6, phpbb_fetch_all 2.0.9, Apache 1.3.28, PHP 4.3.3, and MySQL 4.0.12.
You may or may not have success installing this modification using different versions of the above software. Please report success to me!

STEP ONE
Create a trackback user.

Create a new phpBB user to use for trackback handling. You will need to know what this user's ID number is. You need not provide any information at all except a name, password and email address. If you want your trackbacks to have a nifty user avatar, you could define an avatar. I haven't done this because I think avatars are silly.

STEP TWO
Unzip the pbtb base files into your phpBB directory.

Here's where each file should go:
Code:
pbtb_install.php -> phpBB
trackback.php -> phpBB
trackback_test.html -> phpBB
pbtb.php -> pbpBB/includes
admin_pbtb.php -> phpBB/admin
pbtb_config_body.tpl -> phpBB/templates/subSilver/admin
pbtb_forums_body.tpl -> phpBB/templates/subSilver/admin
pbtb_topics_body.tpl -> phpBB/templates/subSilver/admin


If you want to use different tables than the ones I've chosen, you'll need to edit both pbtb_install.php and includes/pbtb.php.

STEP THREE
Call the pbtb installer.

Log in to your forum as an administrator. Then type the URL to your phpBB forum plus "pbtb_install.php", like so:
Code:
http://www.example.com/phpBB/pbtb_install.php

You will need the userID of the trackback user you created in step one.
Select the defaults for your forum.

* pbtb_user_id
The userID to use for all trackback operations. This user's details will never be linked to from the forum directly.

* trackback_allow_receipt
This is the "master switch" for incoming trackbacks. If set to "No", then all incoming trackbacks will be rejected, regardless of the individual forum or topic settings. If you want to receive trackbacks, you should set this to "Yes".

* trackback_allow_send
The default value for outgoing trackback permissions. If enabled, users will be allowed to send trackbacks to remote sites when they post a new topc.

* trackback_default
The default value for trackback permissions. If a forum or topic does not have an explicitly defined trackback setting, this setting will be used.

* trackback_admin_only
Do you want to restrict trackback functions to moderators and admins only? If set to "No" then trackback functionality will be available to all users, according to per-forum settings. If set to "Yes", then only moderators will be able to access trackback functions.

* trackback_check
Perform security checks on incoming trackbacks. Trackbacks are easily spoofed, and bogus trackbacks could clog up your forum. This setting will perform two checks on every trackback:
1) It will ensure that the URL in the submitted trackback is actually coming from that domain
2) It will ensure that the URL in the submitted trackback is a valid, accessible document
If either of these checks fail, the trackback will be rejected and a message will be logged.

When you're finished, click "Submit". The proper database tables will be created and the default configuration values will be inserted.

Delete the pbtb_install.php file when you're done, please.

STEP FOUR
Modify all the phpBB files to use the new trackback functionality.

This is complicated, and takes a long time. Be careful. Take your time.
BACK UP YOUR EXISTING FILES BEFORE YOU EDIT THEM!

index.php
#
#-----[ OPEN ]------------------------------------------
#
index.pbp

#
#-----[ FIND ]------------------------------------------
#
include($phpbb_root_path . 'common.'.$phpEx);

#
#-----[ AFTER, ADD ]------------------------------------------
#
include($phpbb_root_path . 'includes/pbtb.'.$phpEx);

#
#-----[ FIND ]------------------------------------------
#
                                                        if ( $forum_data[$j]['forum_last_post_id'] )
                                                        {
                                                                $last_post_time = create_date($board_config['default_dateformat'], $forum_data[$j]['post_time'], $board_config['board_timezone']);

                                                                $last_post = $last_post_time . '<br />';

#
#-----[ AFTER, ADD ]------------------------------------------
#
                                                                // *** trackbacks
                                                                if ( $forum_data[$j]['user_id'] == $pbtb['pbtb_user_id'] ) {
                                                                        $last_post .= '<a href="' . pbtb_trackback_url($forum_data[$j]['forum_last_post_id']) . '">' . pbtb_trackback_blogname ($forum_data[$j]['forum_last_post_id']) . '</a>';
                                                                } else {

#
#-----[ FIND ]------------------------------------------
#
                                                                $last_post .= ( $forum_data[$j]['user_id'] == ANONYMOUS ) ? ( ($forum_data[$j]['post_username'] != '' ) ? $forum_data[$j]['post_username'] . ' ' : $lang['Guest'] . ' ' ) : '<a href="' . append_sid("profile.$phpEx?mode=viewprofile&amp;" . POST_USERS_URL . '='  . $forum_data[$j]['user_id']) . '">' . $forum_data[$j]['username'] . '</a> ';

#
#-----[ AFTER, ADD ]------------------------------------------
#
                                                                }

viewforum.php
#
#-----[ OPEN ]------------------------------------------
#
viewforum.php

#
#-----[ FIND ]------------------------------------------
#
include($phpbb_root_path . 'common.'.$phpEx);

#
#-----[ AFTER, ADD ]------------------------------------------
#
include($phpbb_root_path . 'includes/pbtb.'.$phpEx);

#
#-----[ FIND ]------------------------------------------
#
                $topic_author .= ( $topic_rowset[$i]['user_id'] != ANONYMOUS ) ? '</a>' : '';

                $first_post_time = create_date($board_config['default_dateformat'], $topic_rowset[$i]['topic_time'], $board_config['board_timezone']);

                $last_post_time = create_date($board_config['default_dateformat'], $topic_rowset[$i]['post_time'], $board_config['board_timezone']);

#
#-----[ AFTER, ADD ]------------------------------------------
#
                // *** trackbacks
                if ( $topic_rowset[$i]['id2'] == $pbtb['pbtb_user_id'] ) {
                        $last_post_author = '<a href="' . pbtb_trackback_url($topic_rowset[$i]['topic_last_post_id']) . '">' . pbtb_trackback_blogname ($topic_rowset[$i]['topic_last_post_id']) . '</a>';
                } else {
                        $last_post_author = ( $topic_rowset[$i]['id2'] == ANONYMOUS ) ? ( ($topic_rowset[$i]['post_username2'] != '' ) ? $topic_rowset[$i]['post_username2'] . ' ' : $lang['Guest'] . ' ' ) : '<a href="' . append_sid("profile.$phpEx?mode=viewprofile&amp;" . POST_USERS_URL . '='  . $topic_rowset[$i]['id2']) . '">' . $topic_rowset[$i]['user2'] . '</a>';
                } 

viewtopic.php
#
#-----[ OPEN ]------------------------------------------
#
viewtopic.php

#
#-----[ FIND ]------------------------------------------
#
include($phpbb_root_path . 'common.'.$phpEx);

#
#-----[ AFTER, ADD ]------------------------------------------
#
include($phpbb_root_path . 'includes/pbtb.'.$phpEx);

#
#-----[ FIND ]------------------------------------------
#
//
// Go ahead and pull all data for this topic
//
  ...
else
{
   include($phpbb_root_path . 'includes/functions_admin.' . $phpEx);
   sync('topic', $topic_id);

   message_die(GENERAL_MESSAGE, $lang['No_posts_topic']);
}

#
#-----[ AFTER, ADD ]------------------------------------------
#
// Pingback / Trackback collection
/////////////////////////////////////////////////////////
$sql = "SELECT DISTINCT pb.pbtb_id, pb.pbtb_url, pb.pbtb_blogname FROM " . PBTB_TABLE . "
        pb, " . POSTS_TABLE . " p
        WHERE pb.topic_id = $topic_id
        AND pb.pbtb_type = '1'
        ORDER BY pb.pbtb_id";
if ( !($result = $db->sql_query($sql)) )
{
        message_die(GENERAL_ERROR, "Could not obtain pingback/trackback information.", '', __LINE__, __FILE__, $sql);
}
$trackback = array();
if ($row = $db->sql_fetchrow($result))
{
        do
        {
                // trackbacks ordered by post_id
                $trackbacks[$row['pbtb_id']] = $row;
        }
        while ($row = $db->sql_fetchrow($result));
        $db->sql_freeresult($result);
}
/////////////////////////////////////////////////////////
// end trackback collection
/////////////////////////////////////////////////////////

#
#-----[ FIND ]------------------------------------------
#
//
// Okay, let's do the loop, yeah come on baby let's do the loop
// and it goes like this ...
//
for($i = 0; $i < $total_posts; $i++)
{

#
#-----[ AFTER, ADD ]------------------------------------------
#
// modify the postrow[] values with any trackback data we have
        $temp_topic_id = $postrow[$i]['post_id'];
        if ($trackbacks[$temp_topic_id]['pbtb_blogname'] != '')
        {
                $postrow[$i]['username'] = $trackbacks[$temp_topic_id]['pbtb_blogname'];
        }
        if ($trackbacks[$temp_topic_id]['pbtb_url'] != '')
        {
                $postrow[$i]['user_website'] = $trackbacks[$temp_topic_id]['pbtb_url'];
        }
        // end trackback modifications

#
#-----[ FIND ]------------------------------------------
#
        // Handle anon users posting with usernames
        //
        if ( $poster_id == ANONYMOUS && $postrow[$i]['post_username'] != '' )
        {
                $poster = $postrow[$i]['post_username'];
                $poster_rank = $lang['Guest'];
        }

$temp_url = '';

        if ( $poster_id != ANONYMOUS )
        {

#
#-----[ AFTER, ADD ]------------------------------------------
#
// *** trackbacks
                if ( $poster_id != $pbtb['pbtb_user_id'] ) {

#
#-----[ FIND ]------------------------------------------
#
$temp_url = append_sid("privmsg.$phpEx?mode=post&amp;" . POST_USERS_URL . "=$poster_id");
                $pm_img = '<a href="' . $temp_url . '"><img src="' . $images['icon_pm'] . '" alt="' . $lang['Send_private_message'] . '" title="' . $lang['Send_private_message'] . '" border="0" /></a>';
                $pm = '<a href="' . $temp_url . '">' . $lang['Send_private_message'] . '</a>';

#
#-----[ AFTER, ADD ]------------------------------------------
#

                } else {
                $profile = '';
                $profile_img = '';
                $pm_img = '';
                $pm = '';
                }  // end if ( $poster_id != $pbtb['pbtb_user_id'] )

#
#-----[ FIND ]------------------------------------------
#
if ( !empty($postrow[$i]['user_viewemail']) || $is_auth['auth_mod'] )

#
#-----[ REPLACE WITH ]------------------------------------------
#
if ( ( $poster_id != $pbtb['pbtb_user_id'] ) && ( !empty($postrow[$i]['user_viewemail']) || $is_auth['auth_mod'] ) )

#
#-----[ FIND ]------------------------------------------
#
        //
        // Editing information
        //
        if ( $postrow[$i]['post_edit_count'] )
        {
                $l_edit_time_total = ( $postrow[$i]['post_edit_count'] == 1 ) ? $lang['Edited_time_total'] : $lang['Edited_times_total'];

                $l_edited_by = '<br /><br />' . sprintf($l_edit_time_total, $poster, create_date($board_config['default_dateformat'], $postrow[$i]['post_edit_time'], $board_config['board_timezone']), $postrow[$i]['post_edit_count']);
        }
        else
        {
                $l_edited_by = '';
        }

#
#-----[ AFTER, ADD ]------------------------------------------
#
        // *** trackbacks
        $trackback_link = '';
        // insert a trackback link if trackbacks are enabled
        // and this is the first post
        if ( ($i == 0) && ($pbtb['trackback_allow_receipt']) )
        {
                $sql = "SELECT trackback FROM " . PBTB_FORUMS . " WHERE forum_id=$forum_id";
                if ( $result = $db->sql_query($sql) )
                {
                        if ( $row = $db->sql_fetchrow($result) )
                        {
                                $forum_okay = $row['trackback'];
                        }
                        else
                        {
                                $forum_okay = $pbtb['trackback_default'];
                        }
                }
                else
                {
                        $forum_okay = $pbtb['trackback_default'];
                }
                $sql = "SELECT trackback FROM " . PBTB_TOPICS . " WHERE topic_id=$topic_id";
                if ( $result = $db->sql_query($sql) )
                {
                        if ( $row = $db->sql_fetchrow($result) )
                        {
                                $topic_okay = $row['trackback'];
                        }
                        else
                        {
                                $topic_okay = $pbtb['trackback_default'];
                        }
                }
                else
                {
                        $topic_okay = $pbtb['trackback_default'];
                }
                if ($forum_okay && $topic_okay)
                {
                        $trackback_link = "<a href=\"trackback.php?tb=" . $topic_id . "\" title=\"Use this URI to send a trackback\">Trackback</a>";
                }
        }
// end trackback link

#
#-----[ FIND ]------------------------------------------
#
                'DELETE_IMG' => $delpost_img,
                'DELETE' => $delpost,

#
#-----[ AFTER, ADD ]------------------------------------------
#
                'TRACKBACK' => $trackback_link, 

posting.php
#
#-----[ FIND ]------------------------------------------
#
include($phpbb_root_path . 'common.'.$phpEx);

#
#-----[ AFTER, ADD ]------------------------------------------
#
include($phpbb_root_path . 'includes/pbtb.'.$phpEx);

#
#-----[ FIND ]------------------------------------------
#
else
{
        if ( $mode != 'newtopic' && $userdata['session_logged_in'] && $is_auth['auth_read'] )
        {
                $sql = "SELECT topic_id
                        FROM " . TOPICS_WATCH_TABLE . "
                        WHERE topic_id = $topic_id
                                AND user_id = " . $userdata['user_id'];
                if ( !($result = $db->sql_query($sql)) )
                {
                        message_die(GENERAL_ERROR, 'Could not obtain topic watch information', '', __LINE__, __FILE__, $sql);
                }

                $notify_user = ( $db->sql_fetchrow($result) ) ? TRUE : $userdata['user_notify'];
        }
        else
        {
                $notify_user = ( $userdata['session_logged_in'] && $is_auth['auth_read'] ) ? $userdata['user_notify'] : 0;
        }
}

#
#-----[ AFTER, ADD ]------------------------------------------
#
        // *** trackbacks
        if ( ($submit || $refresh) && $is_auth['auth_read'])
        {
                $trackback = ( ! empty($HTTP_POST_VARS['trackback']) ) ? TRUE : 0;
        }
        else
        {
                if ($pbtb['trackback_allow_receipt'])
                {
                        $sql = "SELECT trackback from " . PBTB_FORMS . " WHERE forum_id=$forum_id";
                        if ($result = $db->sql_query($sql))
                        {
                                $trackback = ($db->sql_fetchrow($result) ) ? TRUE : 0;
                        }
                        else
                        {
                                $trackback = $pbtb['trackback_default'];
                        }
                }
        } 

#
#-----[ FIND ]------------------------------------------
#
                        if ( $mode == 'newtopic' || $mode == 'reply' )
                        {
                                $tracking_topics = ( !empty($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_t']) ) ? unserialize($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_t']) : array();
                                $tracking_forums = ( !empty($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_f']) ) ? unserialize($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_f']) : array();

                                if ( count($tracking_topics) + count($tracking_forums) == 100 && empty($tracking_topics[$topic_id]) )
                                {
                                        asort($tracking_topics);
                                        unset($tracking_topics[key($tracking_topics)]);
                                }

                                $tracking_topics[$topic_id] = time();

                                setcookie($board_config['cookie_name'] . '_t', serialize($tracking_topics), 0, $board_config['cookie_path'], $board_config['cookie_domain'], $board_config['cookie_secure']);
                        }

#
#-----[ AFTER, ADD ]------------------------------------------
#
                // *** trackback
                if ($mode == 'newtopic')
                {
                        $sql = "INSERT INTO " . PBTB_TOPICS . " (topic_id, trackback) VALUES ($topic_id, $trackback)";
                        if (!$db->sql_query($sql))
                        {
                                message_die(GENERAL_ERROR, 'Could not insert topic watch information', '', __LINE__, __FILE__,
$sql);
                        }
                }

                if ( ($mode == 'editpost') && $post_data['first_post'])
                {
                        // does this post have a trackback value assigned already?
                        $sql = "SELECT trackback from " . PBTB_TOPICS . " WHERE topic_id=$topic_id";
                        if ($result = $db->sql_query($sql))
                        {
                                if (! ($db->sql_fetchrow($result) == $trackback ) )
                                // post value and database are different; update the db
                                {
                                        $sql = "UPDATE " . PBTB_TOPICS . " SET trackback=$trackback";
                                        $db->sql_query($sql);
                                }
                        }
                        else
                        {
                                // no database entry for this topic yet
                                $sql = "INSERT INTO " . PBTB_TOPICS . " (topic_id, trackback) VALUES ($topic_id, $trackback)";
                        }
                } 
#
#-----[ FIND ]------------------------------------------
#
//
// Notify checkbox - only show if user is logged in
//
if ( $userdata['session_logged_in'] && $is_auth['auth_read'] )
{
        if ( $mode != 'editpost' || ( $mode == 'editpost' && $post_info['poster_id'] != ANONYMOUS ) )
        {
                $template->assign_block_vars('switch_notify_checkbox', array());
        }
}

#
#-----[ AFTER, ADD ]------------------------------------------
#
// *** trackbacks
//
// Trackback checkbox - only show if user is logged in, and trackback settings allow
//
// first, are trackbacks enabled?
if ( $userdata['session_logged_in'] && $is_auth['auth_read'] && $pbtb['trackback_allow_receipt'] && ( ($mode == 'newtopic') || ($mode == 'edit')) )
{
        // are trackbacks enabled for this forum, or is the default setting permissive?
        $sql = "SELECT trackback FROM " . PBTB_FORUMS . " WHERE forum_id='" . $forum_id ."'";
        $result = $db->sql_query($sql);
        $row = $db->sql_fetchrow($result);
        if ( ($row == '1') || ( $pbtb['trackback_default']) ) {
                // are trackbacks limited to moderators?
                if ( (! $pbtb['trackback_admin_only']) || $is_auth['auth_mod'] ) {
                        $template->assign_block_vars('switch_trackback_checkbox', array());
                } // if admin check
        } // if forum or default check
} // if overall check

#
#-----[ FIND ]------------------------------------------
#
        'L_DISABLE_SMILIES' => $lang['Disable_Smilies_post'],
        'L_ATTACH_SIGNATURE' => $lang['Attach_signature'],
        'L_NOTIFY_ON_REPLY' => $lang['Notify'],
        'L_DELETE_POST' => $lang['Delete_post'],

#
#-----[ AFTER, ADD ]------------------------------------------
#
        // *** trackbacks
        'L_TRACKBACK' => $lang['Trackback'],

#
#-----[ FIND ]------------------------------------------
#
        'S_HTML_CHECKED' => ( !$html_on ) ? 'checked="checked"' : '',
        'S_BBCODE_CHECKED' => ( !$bbcode_on ) ? 'checked="checked"' : '',
        'S_SMILIES_CHECKED' => ( !$smilies_on ) ? 'checked="checked"' : '',
        'S_SIGNATURE_CHECKED' => ( $attach_sig ) ? 'checked="checked"' : '',
        'S_NOTIFY_CHECKED' => ( $notify_user ) ? 'checked="checked"' : '',

#
#-----[ AFTER, ADD ]------------------------------------------
#
        // *** trackbacks
        'S_TRACKBACK_CHECKED' => ( $trackback ) ? 'checked="checked"' : '', 

language/lang_english/lang_admin.php
#
#-----[ FIND ]------------------------------------------
#
//
// That's all Folks!
// -------------------------------------------------

#
#-----[ BEFORE, ADD ]------------------------------------------
#
//
// Pingback/Trackback
//
$lang['PBTB'] = 'Pingback/TrackBack';
$lang['PBTB_General'] = 'Configuration';
$lang['PBTB_Forums'] = 'Forum Settings';
$lang['PBTB_Topics'] = 'Topic Settings';
$lang['PBTB_Config'] = 'Pingback / Trackback Configuration';
$lang['PBTB_General_Explain'] = 'Here you can configure overall pingback and trackback settings.';
$lang['PBTB_Pingback_settings'] = 'Pingback Settings';
$lang['PBTB_Trackback_settings'] = 'Trackback Settings';
$lang['PBTB_Other_settings'] = 'Other Settings';
$lang['PBTB_pb_receive_allow'] = 'Receive Pingbacks';
$lang['PBTB_pb_receive_allow_explain'] = 'Turn this off to completely disable receipt of incoming pingbacks.';
$lang['PBTB_pb_send_allow'] = 'Send Pingbacks';
$lang['PBTB_pb_send_allow_explain'] = 'Turn this off to completely disable sending pingbacks.';
$lang['PBTB_pb_default'] = 'Pingback Default Setting';
$lang['PBTB_pb_default_explain'] = 'Do you want to enable pingbacks by default on new posts?';
$lang['PBTB_pb_admin_only'] = 'Pingbacks for admins only';
$lang['PBTB_pb_admin_only_explain'] = 'Restrict per-post pingbacks to admins only?';
$lang['PBTB_tb_receive_allow'] = 'Receive trackbacks';
$lang['PBTB_tb_receive_allow_explain'] = 'Turn this off to completely disable receipt of incoming trackbacks.';
$lang['PBTB_tb_send_allow'] = 'Send trackbacks';
$lang['PBTB_tb_send_allow_explain'] = 'Turn this off to completely disable sending trackbacks.';
$lang['PBTB_tb_default'] = 'Trackback Default Setting';
$lang['PBTB_tb_default_explain'] = 'Do you want to enable trackbacks by default on new posts?';
$lang['PBTB_tb_admin_only'] = 'Trackbacks for admins only';
$lang['PBTB_tb_admin_only_explain'] = 'Restrict per-post trackbacks to admins only?';
$lang['PBTB_tb_check'] = 'Check incoming trackbacks?';
$lang['PBTB_tb_check_explain'] = 'Check incoming trackbacks to prevent spoofing attempts?';
$lang['PBTB_user_id'] = 'Pingback / Trackback UserID';
$lang['PBTB_user_id_explain'] = 'This is the UserID that will be used to insert pingbacks and trackbacks into the database.';
$lang['PBTB_Perms_Title'] = 'Per-Item Permissions';

$lang['PBTB_Pingback'] = "Pingback";
$lang['PBTB_Trackback'] = "Trackback";

$lang['PBTB_Forums_Title'] = 'Forums Administration';
$lang['PBTB_Forums_Explain'] = 'Here you can enable or disable pingbacks and trackbacks for each forum in your board.'; 

language/lang_english/lang_main.php
#
#-----[ FIND ]------------------------------------------
#
//
// That's all Folks!
// ----

#
#-----[ BEFORE, ADD ]------------------------------------------
#
// PINGBACKS / TRACKBACKS
$lang['Trackback'] = 'Allow Trackbacks on this topic'; 

templates/subSilver/viewtopic_body.tpl
#
#-----[ FIND ]------------------------------------------
#
                        <tr>
                                <td width="100%"><a href="{postrow.U_MINI_POST}"><img src="{postrow.MINI_POST_IMG}" width="12" height="9" alt="{postrow.L_MINI_POST_ALT}" title="{postrow.L_MINI_POST_ALT}" border="0" /></a><span class="postdetails">{L_POSTED}: {postrow.POST_DATE}<span class="gen">&nbsp;</span>&nbsp; &nbsp;{L_POST_SUBJECT}: {postrow.POST_SUBJECT}</span></td>
                                <td valign="top" nowrap="nowrap">{postrow.QUOTE_IMG} {postrow.EDIT_IMG} {postrow.DELETE_IMG} {postrow.IP_IMG}</td>
                        </tr>

#
#-----[ IN-LINE REPLACE WITH ]------------------------------------------
#
                        <tr>
                                <td width="100%"><a href="{postrow.U_MINI_POST}"><img src="{postrow.MINI_POST_IMG}" width="12" height="9" alt="{postrow.L_MINI_POST_ALT}" title="{postrow.L_MINI_POST_ALT}" border="0" /></a><span class="postdetails">{L_POSTED}: {postrow.POST_DATE}<span class="gen">&nbsp;</span>&nbsp; &nbsp;{L_POST_SUBJECT}: {postrow.POST_SUBJECT}</span></td>
                                <td valign="top" nowrap="nowrap">{postrow.TRACKBACK} {postrow.QUOTE_IMG} {postrow.EDIT_IMG} {postrow.DELETE_IMG} {postrow.IP_IMG}</td>
                        </tr>

templates/subSilver/posting_body.tpl
#
#-----[ FIND ]------------------------------------------
#
                  <!-- BEGIN switch_notify_checkbox -->
                  <tr>
                        <td>
                          <input type="checkbox" name="notify" {S_NOTIFY_CHECKED} />
                        </td>
                        <td><span class="gen">{L_NOTIFY_ON_REPLY}</span></td>
                  </tr>
                  <!-- END switch_notify_checkbox -->

#
#-----[ AFTER, ADD ]------------------------------------------
#
                  <!-- BEGIN switch_trackback_checkbox -->
                        <td>
                          <input type="checkbox" name="trackback" {S_TRACKBACK_CHECKED} />
                        </td>
                        <td><span class="gen">{L_TRACKBACK}</span></td>
                  <!-- END switch_trackback_checkbox -->

STEP FIVE
Set per-forum permissions.

You probably don't want trackbacks coming in for every single forum. You can set per-forum trackback permissions easily from your Administation Panel.

Forums and topics inherit the trackback_default setting until you explicitly assign per-forum or per-topic permissions.

Topics are restricted by the trackback setting for the forum they reside in.

For example, if you have a forum called "Announcements" that is for staff announcements only, you can set the "Announcements" forum's trackback setting to "No". Even if you enable trackbacks on a new topic in the "Announcements" forum, that topic will reject incoming trackbacks because the forum setting prevents it.

You can enable trackbacks for all of your existing posts by simply setting the trackback_default to "On". For all forums that accept trackbacks, their topics will now accept trackbacks.

If you wish, you can set per-topic settings from the Administration Panel. This shows every topic, so it may be impractical on really popular boards. If you lock a topic, that will prevent that topic from receiving trackbacks. I figure if you don't want comments posted, you probably don't want trackbacks posted either.

STEP SIX
Test!

Get some friends who run blogs to try to send trackbacks to you. If you don't know anyone who runs such a blog, I've included a test file, trackback_test.html. Edit this file, and point the trackback URL to a trackback-enabled topic on your forum.

NOTE: You may want to disable trackback_check when using trackback_test.html, since the submitting IP address (your's!) probably won't be running a web server that accepts trackbacks.

When you're confident that things work, delete the trackback_test.html file. I don't think there are any specific security concerns for keeping it, but there's not sense leaving it if you're not going to be using it.


