I was just about to post the same question...
I too have an XP2500+, currently running at 166 mhz and clocking at 1.836 Ghz. Idle temp is 52c and underload, she jumps to 60c... I never saw my old Duron go above 45c so 60c has me shaking in my seat. I know kill temp is like 80+c but I sure don't want to dance on the edge.
I am using the stock HSF that came in the retail package. I can't say I am very impressed with the performance. My case is very well ventilated and my system board temp seldom rises above 30c. I want to get my CPU running as cool as possible without resorting to Liquid Nitrogen, liquid cooling, or placing my system in a fridge.
Can anyone recommend a HSF that is good for keeping the temp down below 50c... Preferably in the $50 CAN range.