NVidia GeForce 8800 GT

I have just started playing a game on WIN XP which takes high end pc's to run. This caused my pc to turn itself off and then struggle to restart. I first thought that my power source 550 watts was insufficient and installed new power source Corsair 750w. This wasn't the problem, my Nvidia GeForce 8800 GT is overheating, at least Duel Core centre reports this and shuts down my pc. However, the resting temp is 47c and intensive gaming takes it up to around 82c , whereapon my rig shuts down.
My question , are these temps excessive or is my dual core centre set wrongly and how should I adjust it. Any help please.
47 degrees is fine at rest, 82 is not.

Check the fan on your board.. make sure it's not clogged and is free of dust, dirt, and other particles.