The "Keeping an AMD processor cool dance" is something I've been doing for a while. It can be (at the same time) fun, frustrating, and expensive. But for those of us who like a good technical challenge, we stick with it
All of the systems in my house are Athlons running in a fairly restrictive MicroATX case (the Palo Alto PA-450, to be exact). Stock, this case doesn't have ANY case fan mountings, it just uses the power supply to vent waste heat. Obviously, not an ideal cooling setup, but it's an otherwise great case, so I stick with them.
First, the original Athlon XP's (Tbird) run hot. Not QUITE as hot as the older Athlon's like the 1400, but pretty close. The first change I would make if you have an older CPU like that is to upgrade to a Thoroughbred "B" core CPU. I went from an 1800+ TBird to a 2400+ Tbred B and my core temps (read from the die) dropped nearly 10C. Second, take a look at the base of your heatsink. If it isn't mirror smooth, lap it
. Personally, I have used anything from the stock AMD heatsink to a Thermalright SK7, and they all get the job done. I have seen my temps drop as much as 3C by lapping my heatsink base, properly reapplying thermal compound, and then properly installing the heatsink. Third, make sure your heatsink fan is blowing in the proper direction. Changing from "suck" to "blow" or vice versa can drop temps another couple of degrees, but it depends a bit on the fan and the sink, so play around with it. Fourth, look at other heat producers in your system, like the northbridge, your video card, your hard drives, and your optical drives. I had a Plextor 16/10/40 in my machine and it had this terrible little 40mm fan...was the drive creating that much heat that it needed an exhaust fan? I replaced the drive with a Samsung SM-348 and (a) ended up with a quieter, better drive and (b) my case temps dropped 1C. Fifth, look at your cable routing. Obviously, make sure nothing is blocking airflow; rounded cables help make it easier to keep the cables out of the way (IMO). I took the rather extreme step of cracking open my power supply and snipping/insulating all of the power leads that I didn't need (usual death warnings apply here). Not sure if it lowered temps, but I'm sure it didn't hurt. I replaced my waffle-style northbridge heatsink with a Zalman heatsink -- if you get rid of the heat faster/more efficiently, it should keep things cooler. And, as always, keep your case, heatsinks, fans, power supply, and filters dust-free.
There are lots of ways of decreasing case temps without increasing noise levels, but it does take time, patience, and sometimes money.