I've recently completed the instalation of my second computer, wich is an Athlon Xp 1.7 (wich is hot as hell when running), and made the folowing experiment:
I bought a fan (running at 3000 RPM) for almost nothing and put it in the place of the cooler (running at 4500 RPM). The thing is that the fan is slower but it is larger, wich made the temperature drop about 10 degrees celsius! I don't have to mention that the whole computer is much quieter now, and it could be even more if I have bought a low-noise fan instead of a regular one. This is the second experiment I made using fans, and the result of the first experiment was exactly the same, a 10 degree drop in temperature and a quieter computer.

I really would like to know if someone has tried it before with good results either.