Older versions required register_globals to be "on", and that's what happened when it wasn't. The current version is 2.7.1 and no longer relies on register_globals.
I'm pretty sure that register_globals do not have to be on for the forum. Have you installed other plugins that are not from portalparts and have they worked?
I have a feeling you probably forgot to move the lib-portalparts.php file to the system directory...
Only problem now is that my whole geeklog website is now blank
Thu 20 Nov 2008 03:42:43 PST - Attempting to give all users in Root group access to forum admin group
Thu 20 Nov 2008 03:42:43 PST - Registering forum plugin with Geeklog
Thu 20 Nov 2008 03:42:43 PST - Succesfully installed the forum Plugin!