Riva Tuner saves another person
Download Riva Tuner from here:
Install it and then load it up
Click on the bottom of the two Customize button, and then choose the first icon along (says "System Settings" when you put the cursor over it).
Now, go to the Fan tab, and lower the top one to 40%, the next one to 80% and the bottom one to 90%. Finally, load up a game, minimize after an hour or so, and check the temperature - if the temperature is too high, raise the fan speed, if its extremely low, you can lower it a bit more