LYCUK, сторока 18
вроде так
$sql = mysql_query("select cms_forum_files.* from `forum` join `cms_forum_files` on cms_forum_files.del=0 and forum.id=cms_forum_files.post and forum.from='" . $_GET['list'] . "' order by `cms_forum_files.id` desc limit " . $start . ", " . $total);