I'll just take a stab here, not sure if it will work. Leave Norton Systemworks out of your system. That program was okay with Windows 98 or Me but it's almost completely useless with XP. If you want a better Defragmenter use Diskeeper, it's better and faster. Systemworks takes too much drive space and resources.

I have a friend with a similar notebook to yours. His freezes when playing games which is a Video-Driver issue. Do you remember what exactly you are doing when the freezes happen?