4
The problem seems to be that XOOPS is using the old-style global variables for accessing values from forms:
$HTTP_SERVER_VARS instead of $_SERVER
$HTTP_POST_VARS insteadd of $_POST
a zillion of places to change if someone (like I) have to get it running on a PHP 5 server. So, installation docs should say it's only compatible with PHP 4, not newer (yet).
/PeO