Yeah, my experience is this can't be debugged at the windows O/S level. By definition it is either a hardware failure or a kernel mode driver fault. Heat can be the culprit, but given that you have a 6800GT I suspect you have the problem I described earlier. It is extremely random in nature, and as far as my experience it only happens with games that really exercise the 3D functions. I had it most often with BF2, and sometimes went weeks between espisodes, other times it happened every session. Since you're on nForce 4 (it happened mostly with nF3 and nF4) my conviction is even greater.
You can try searching for an answer, but I don't know of one that is foolproof. This has been going on for over five years, and people have changed everything you can think of. I upgraded to a 7600GT and haven't had a lock-up since.