heatsink fan spinning low on pc probe and bios indicators, replace?

my system runs anywhere fom 32 to 36 when idle and i had noticed it creeping up a bit. my heatsink fan (stock intel) is only spinning around 1000 rpm and the core temp is now around 48-49. i think the heatsink fan is dying, since both pc probe and my bios agree on the fan speed. So, a few questions.

What is a good heatsink/fan for a socket 478 2.8 gz northwood chip? the mb model is below? I don't have any crazy stuff in the case so space isn't an issue.

How do I know it's really the fan going kaput and not a controller on the motherboard?

I know my friend has this little sucker on his 2.8 northwood. Its a cheapie but a goodie.
http://www.newegg.com/Product/Product.asp?Item=N82E16835106606

But you cant go wrong with anything from thermaltake

You could always get a 3-pin to 4-pin molex adapter, and run the fan directly off the main line. Or try another fan.

A good brand name is coolermaster. I have one on my oced northwood and it is always under 40c unfortunately, they dont make the cooler i have anymore.

If I were you I'd try it on a different PSU just to be 100% sure, and before you toss the fan try cleaning it with a cotton swab and some alcohol.
Fans that aren't cleaned once in a while can get so dusty that they completely stop functioning.