below 60C is fine.
65 and below should still be good, but may be a little hot.
you can get a better case, better fan, clear off DUST inside your computer (if any)
or if you want, what most people would try, is using some thermal products
like thermal grease, you put a dab of it on your processor (top, center) and run your computer
it'll heat up, and spread out, and basically just stay there.
it can cool your Cpu down a good bit, some people have gotten it 13 degrees LOWER, before.
which is great.
i don't know any specific names of the products, though.
*gags at the very mention of Thermal Take products* I've had several Thermal Take coolers, and all of them have ta some point died. The chrome Orbb I wa susing on my old Athlon 900 just died within 2 minutes (all I did was run WinAmp!!) And the Volcano 2 i bought near casued the chip to explode.
I have an Asus A7V 133 board, and I know for a fact that all Asus boards CPU temp sensors read alot higher than they actually are, the'yre about 5 - 6 degrees out (they read hig) in some severe cases they are as much as 10 degrees out.
Get yourself a Cooler Master Heat Pipe cooler, thats what I'm running currently, dropped my cpu temp of 65 deg C down to 45 Idle, and 49.5 full load, bare in mind the prob with the Asus sensor and software and it's cool as a cucumber. The heat sync is pure copper, which is the best for cooling a CPU, on top of that there's a 7200 RPM Delta fan (yeah I know deltas sound like vacuum cleaners) but the benefit you get form the cooling on your chip out weighs the disadvanates of the noise, and I've found with mine that as the weeks pass by the fan get quieter!!
Behemoth - I have been using the AS3 and a Volcano 7 w/ speed control. I havnent had a problem with it at all, and its keeping my computer nice and cool. Right now, System temp is 24C, CPU is 31C idle, load raises the CPU temp up about to 37 is the highest. Thats not bad at all for an athlon xp 2000+