It's a pain, as the audio stops as well, the freezes last for about a second or so. As I used this machine for producing music, and jitters in the audio stream are bad (tm).
Freezes for one sec then starts working normally again? then freezes again after some random time?
Or does it freeze completly so that reset is only escape?
I had a very similar problem like this... Turned out to be the drivers for the promise raid/ultra cards... the same thing happened on both of them... i think the ide bus would reset, which caused the whole system to freeze up completly for a sec and then work normally for another min or so before it happened again..
Installing the older version of the drivers completly solved the problem.
EDIT:
might be a dying disk also