I'm running an Athlon XP 1800+ (1.5GHz), CPU temp is on average 55C, maximum 61C. If the CPU works stabily at a temperature, don't attempt to 'fix it'. Just make sure airflow is good out of the case so that the temperature of the CPU is affecting other components as little as possible.
(dual fan PSU, single fan on CPU heatsink@ 5.8K RPM, it would be nicer if it were quieter, but not unbearable)
