Hmm you may have explained a problem of my own!
I was experiencing 3-4 BSOD's/errors a day before, and I put this down to bad RAM (even though no errors were shown in Memtest - because I didn't leave it running for more than a few hours).
I had overclocked 1.8Ghz Opty to 2.4Ghz (yes, a 600Mhz o/c!), and also overclocked/unlocked the graphics card. It wasn't quite stable at 2.4Ghz (even though I knew I should be able to push it much further), so I was running it near 2.3Ghz - and this was when all of the BSOD's occured. I left it because I thought I'd get the RAM replaced, but days turned into weeks, and it was only the other day when I decided to cut it back even further to near 2.2Ghz.
Result, far fewer BSOD's - 1 every 2/3 days or so (and I use the machine 24/7).
Now... I wonder if the PCI is unlocked!
I haven't checked for now (can't be bothered to restart), but if it is it could explain errors occuring with the graphics card too.
Edit: Had a look and the PCIE is locked to 100Mhz so I wonder if I should lower that... guess I better find out!