[Makinus]

I had the exactly same problem that you had and found 2 main (and completely unrelated) causes for it: 1. One of my RAM has gone bad, just replaced it but the problem continued, while in a less severe way (a freeze every eight hours or so)... 2. I discovered, while navigating the internet, that my dual processor had some incompatibilities with old programs (mostly old games) that causes errors in the processor that would increasingly clutter the cpu without anything appearing in the xp monitoring... i found a 3rd party "patch" that resolved the problem and after aplying it never had any problems again...

After some digging it appears that nearly all dual processor CPUs have some problems (some more other less serious) with programs made before they are created, mainly games...