You didn't say if you did an upgrade install of XP or a clean install.
An upgrade installation would carry over the problems.
XP works best when clean installed.
Other possible causes are Spyware/Parasites from running Kazaa/Imesh/P2P Networks.
Scan with Ad-Aware, SpyBot, Stinger & CWShredder to make sure your PC is not infested with spybots.
Are the BIOS & motherboard drivers installed as well as all device drivers?
My computer freezes on an irregular basis, like once a day, sometimes every hour or so. It had windows ME when I purchased it. I upgraded to XP but no different. I also upgraded the RAM from 64 to 256, no different. I took the cover of thinking it was a heat problem no different. The fan works ok.
Any other ideas? this is a compaq desktop 750MHZ.