flashing the bios most likely wouldn't help.. it sounds either heat related or OS related.. if it passes memtest (is that a full run on 12 passes or just 1 pass?) and your still crashing when you load games, you may need a re-install or repair from OS disc? (boot from it and select repair instalation instead of new install/upgrade)
I only did 1 pass, as I thought that it was just going to keep running the same tests. Now you've mentioned the 12 passes, I'll dig out the disc and do 12.
Right, I'm not a computer whizz, but here's my contribution:
Recently got a new rig from chaos, sexy as it is, getting the BSOD fairly often during gameplay (couple of times out of gameplay, but those have been separate issues) with the same issue of "Page fault in nonpaged area".
Came to the conclusion that it was a GPU issue with the card overheating (proved when we logged the heat getting into the 90's)
Since then, have sorted by having 2 profiles for gaming and normal use.
Gaming - high-ish GPU overclock but fans on 100%
Normal - low-ish GPU overclock with fans at approx 35%
I would recommend trying either underclocking your graphic card, or turning up the fan speed
As I say, my knowledge is limited, but may be of use

Thanks for your help, all suggestions appreciated =) any of you guys know how applicable this solution is?