8800GTS problem with gaming/dualscreen on Vista

I have a really annoying problem regarding my video card and Vista.

Im on a E6750 processor, P4P800 motherboard, Vista Premium 32bit, 8800 GTS , 4GB DDR2, 650w PSU, etc.

So here's the problem :

Im using two 22" Samsung widescreens. Both are on 1680 resolutions. I'm on the 178.13 drivers (the latest ones).

So, I launch World of Warcraft. Then, I switch back to my 2nd screen to open a movie with mediaplayerclassic. From time to time it works, but it can also crash : my screen starts to blink, then it alt-tab to desktop and I get a message like "The driver stopped working but is now working again" (or something like that).

Then, I need to close the game that I was playing trough the task manager. But the crap is not over because I need to reboot my computer because even if I try to relaunch the game, it's just gonna stall or have excessive tearing/skip.

I've tried to reinstall different drivers, sweep them, clean install, etc etc. It's always doing it, no matter what. Could I have a deffect card? Could it be overheating?

What do you think??

Thanks ALOT!!