Hi,
the lower the better, but mine is running at 33C or 38C with no programs running and goes up to 50 or 55C under heavy load. It depends also on the room temperature (and case temperature). I think staying below 60C will be save. I have installed an Alpha 6035 Cooler on my CPU, which is an Athlon 800 running at 1100. I also have a lot of casefans installed which caused the case temperature to drop to almost room temperature. Without casefans all the hot air will stay inside and the CPU temp rises even higher. Also an increased core voltage will cause high temperatures.
I think that you should be able to keep your CPU below 60C.
My geforce2MX also gets very hot, so i installed some coolers on it too. I could touch it for a little while but then it would get too hot to touch pretty quick. With the coolers it is much better. I can't tell you a temperature about this though...
i hope i was of any help..
Bye!