[DSanchez]

Ah ha! I found the problem. TABLE_PREFIX was missing from get_threads.php. I modified it like so:

$dataQuery = "SELECT t.*, p.pagetext FROM " . TABLE_PREFIX . "thread t LEFT JOIN "
        . TABLE_PREFIX . "post p ON ( p.postid = t.lastpostid ) WHERE t.forumid = "
        . $fid . " AND t.open = 1 AND t.visible = 1 ORDER BY t.lastpost DESC LIMIT "
        . $offset . "," . $rows;

And also in get_posts.php:

dataQuery = "SELECT * FROM " . TABLE_PREFIX . "post WHERE ThreadID = " . $threadid . " AND visible = 1 ORDER BY Dateline DESC LIMIT " . $offset . "," . $rows;