[kh99]

OK, try this:

$find = '<h2 class="forumtitle"><a href="\' . vB_Template_Runtime::linkBuild("forum", $forum) . '">\' . $forum['title'] . \'</a></h2>';
$replace = '
 <h2 class="forumtitle"><div id="scanu"><a title=\'<scanu>' . $forum['description'] . '</scanu>\' href="' . vB_Template_Runtime::linkBuild("forum", $forum) . '">' . $forum['title'] . '</a></div></h2>

Edit: well, the replace code there isn't right, but the point is that you need to escape all single quotes in the string you're trying to match. You seem to have escaped the quotes in the string you're adding, but not in the string you got from the compiled template.