95% likely that it is faulty ram. The reason it will mostly crash during gameplay is because that area of memory is not being accessed, then when games are being played its using more of your ram so more likely its going to try and access the fault section of RAM.
Try taking 1 stick of RAM out and seeing if you get errors. If you do, put in the other stick of RAM. It's not likely that both are faulty.
If it is a driver fault (by some small chance) use
BlueScreenView. It's a nifty little program which will determine the file at fault.
But note that ntsokrnl.exe, hal.dll and your video drivers (nvidiaview.exe or ati*something*.exe etc.) will be seen as the cause of the fault in BlueScreenView if the actual cause is your RAM because these files are usually the ones accessing the corrupted sector of ram as it BSOD's.
Other than those files, you might come across a faulty driver like pksec.exe or something which will lead you to the cause of the BSOD's.
But it's still extremely likely that it is faulty RAM.
Posted on Tuesday, 30th August 2011