Well 8600GTS is a low-end card for gaming but if you want to keep it,then download rivatuner and tweak the fan speed.
However,i would recommend getting a better card like HD 5770
BTW,what's your PSU ?
I actually did rivatuner thing and it seems to be at 100% or I'm doing smth wrong...
HD 5770 looks good, although I would love to stay at $100-130 range since gaming is not a big issue for me, just a couple of hours not each day.
My PSU is 400w foxconn