Bona Fide Reviews published a beginner's guide to air cooling your computer

Computers are getting faster and faster every week. Faster, denser CPU's, motherboards, and video cards are coming out all the time and all of these things generate more and more heat. It used to be that you could count on the little fan in your power supply to suck the hot air out and keep everything humming along just fine. Try that on some machines today and you'll end up with a heap of smoking silicon and plastic and a decidedly dull, blank monitor to stare at.

A Beginner's Guide to Air Cooling Your Smokin Hot Computer