You can also download a program that can manage the speeds of the fans.
SpeedFan is a good one, it doesn't work with all computers, but works with quite a few. http://www.almico.com/speedfan440.exe
There are other fan controllers on the market, you just have to research which ones will work on your computer.
Personally, I have a Macbook Pro so I have to use a program called FanControl on the mac side to set a range. It's a bit more convenient than a a program that just sets a speed but it also doesn't allow me to specify specific speeds at specific times.