I'n playing with my brand new 8800 GTS 512MB and can't figure out how to change the fan speed. In trying to make it complain a bit with trhdrible.exe to stress the GPU I see the temp go up to 70 deg C but the fan speed doesn't change. At idle it seems to be around 50. In looking at the NVIDIA Control Panel the Cooling GPU item is grayed out and the fan is set to 37%. Moving the slider doesn't have any effect.

Hey! Guess what? The fan speed doesn't change until you click the "Apply" button. :-) Guess I'll find an acceptable noise level and leave it.

Guess what? 70C is ok for a GPU temp. What brand card do you have? All brands have different ways they control fan speed. I have an xfx and they tend to lean toward more aggressive fan profiles, ie. it hits 60% at 65C. Others lean toward lower noise so they don't kick on to 50% until 70C to keep noise down. Honestly with the 8800GTS you should just leave the auto fan go. They run pretty cool compared to other cards regardless so don't monkey with it.

It's a BFG. I thought I read they stick the fan at 37%. So am I safe in assuming the fan will increase in speed if the temp gets up there?

Yes. Every brand has different settings. 70C isn't that bad I mean I get to 65C and they say XFX is pretty aggressive with the fan speed profile.