I would highly suggest you switch to a more reliable script. PHP-Nuke is made up of bloated code, a mess of queries, and it is a server killer.
I'll just list some alternatives:
Virtuanews (
http://www.virtuanews.co.uk)
MkPortal (
http://www.mkportal.it)
Subdreamer (
http://www.subdreamer.com)
Mambo OS (
http://www.mamboserver.com)
vBadvanced (
http://www.vbadvanced.com)