No matter how well-designed your case is, there is no way the one fan in the Power Supply(PSU) is enough to keep your system cool. A 1.2 GHz Athlon generates an awful amount of heat, and all the CPU fan does is moving it away from the CPU. However, the hot air is replaced with air from inside your case. Since with a standard heatsink/fan cooling solution your CPU can only be as cool as the air inside your case, it is VERY important to add in extra case fans that move air through the case.
Like I said before, the one single fan in the PSU in insufficient for that purpose, especially for the powerhouse you have. Most people have at least one, but more often two extra case fans. It is often suggested that you attach one intake fan to the front of your case (most modern cases are made to accept a front fan), which draws in the cool air from outside. You should also add an exhaust fan, attaching it to the back of the case (from the inside of course
). Newer cases also have a spot in the back for an extra fan. It is usually near the CPU so that it draws out the hot air generated by your processor, not allowing it to heat up other components.
If you are lucky, you have a PSU with bottom intake, meaning that the power supply has holes (or possibly even a fan) right above the CPU, which is the ideal solution for getting the hot air out of your case. You might want to consider getting such a power supply, but getting an extra fan instead is much cheaper of course, and it gets the job done.
Anyway, my point is that you should definitely get two, or at least one extra fan. Oh, and do yourself a favour and get a better model (preferably a ball-bearing fan), unless you want to buy a new one in less than a year. Cheap fans also tend to be noisier, making your machine sound like there is a Boeing 747 under your desk.
AMD has a document up on their site about ideal cooling. They pretty much say the same things. Here's a link:
<A HREF="http://www.amd.com/products/cpg/athlon/pdf/cooling_guide.pdf" target="_new">http://www.amd.com/products/cpg/athlon/pdf/cooling_guide.pdf</A>
Cheers
Scott me up, Beamie!!!
(old one, but hey, it's still funny)