I have an Athlon XP 2400+ on a Biostar M7VIG Pro with 256DDR in an Antec case with a dual cooled power supply and a large 120mm fan in the upper rear of the case. The system has been burning in for almost 12 hours now.
The cpu temp is 48-50C and the cpu fan speed is 4100 RPM. Both of these values seem high? Forgot system fan 1800 RPM.
Also the Antec power supply as a -12V reading of -13.10 and I have no idea if this will affect the life of the system or CPU? When I ran the HW doctor program that came with the MB it gave me a WARNING message saying it was outside the limit. I adjusted the limit until the warning message went away.
Those temps aren't bad but they aren't good either. Is it hot where you are right now? Where are I'm it's around 80-90 F. My temps too were a little high due to the weather (high pressure not too much air circulating around). Now that the weather is better I'm getting lower temps. You should check that you installed the HS right and if using thermal grease like AS3 you should re-apply it. As a last resort buy a new HS.
About the voltage that certainly is not good. I think that it should only be a 5% of error but I'm not totally sure. I have a generic PSU 350W and the -12V is @ 12.56v on average.