If you're feeling froggy you can diagnos the memory dump file and see whats happening when it blue screens. See here:
http://forums.majorgeeks.com/showthread.php?t=35246
Also, if you're getting mem errors when running mem check it doesn't always mean the RAM's bad, could be the processor or something else. Since it seems to happen when the PC is under stress (gaming etc) my first guess would be undervoltage. Maybe increase the voltage on the processor and memory a little. Just some thoughts to pile on the others.