I tried what you suggested there, but it doesn't seem to work. The page is a custom 404 error page, if that makes any difference.
I enter:
<?php include($_SERVER['DOCMENT_ROOT'] . '/layout_2003/page_top.php'); ?>
but it doesn't work.
Works when I go specifically to the file's page (http://www.theinsaneasylum.com/404error.php), but if I enter something random (http://www.theinsaneasylum.com/dfslkj.php) it doesn't work. Actually, if the random file's extension is php, it just shows a white screen, but for anything else, it shows the page without working PHP tags.
This is very odd.