MacBook Pro (Late 2008) crashes when playing a game in bootcamp, yet is fine when the battery is removed. Help!

Hi, i run a game in bootcamp on the lowest possible settings, and it will usually freeze on me about 10-15 minutes in; the screen blacks out and short audio snippets loop over and over.

However, removing the battery makes the game run perfectly for hours. Any ideas?

The battery (and everything else) has passed the Hardware Test. I have taken the notebook to the Geniuses, who ended up replacing my CD-Drive (which was also faulty), and cleaning out the inside; unclogging the fans etc. Although the notebook does seem to stay cooler, it still crashes.

It doesn't matter whether the battery is charging, or completely full... it still crashes when both the battery and adapter are connected.

Also, unplugging the adapter and running from the battery also makes the game run smoothly, however this isn't ideal as the computer can shut off at any minute without warning.

I cant seem to pin-point what this could be, except perhaps something to do with too much power, perhaps? Or a possible graphics card error? (in bootcamp i think its just the 9600M GT card is running).

Note: I have updated to the latest bootcamp version, and installed all drivers (i think, definitely the main ones, anyway).