For some Athlons, this ain't easy. I know 'cause I went down that route. I've had cpu coolers gathering dust... Eventually, I gave them away.
Look for LVCool. It does something to one of the motherboard chips (I don't remember which) and results in, in my case, a drop of 15c from 45 to 30! Stick it in rc.local or some other startup script and it does the job just great.
I think that it might actually be available in the Dag repository...
-- Dylan Parry http://www.webpageworkshop.co.uk - FREE Web tutorials and references