http://www.newegg.com/Product/Product.aspx?Item=N82E16835425007&nm_mc=OTC-Froogle&cm_mmc=OTC-Froogle-_-Mem ory+++Chipset+Cooling-_-VIZO+Technology-_-35425007
($13.99)
You gotta get that fan off the chipset, and put a new one on. I've used this one as a good replacement on an Asus A8N-e series board (defective fans) running an Athlon 64 FX55 - works nice.
I also have used this one on the same board:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835118014&cm_re=Zalman_chipset-_-35-118-014-_-Product ($9.50)
The zalman one, though it looks nice, I would never buy again. It's a real pain in the ass to install - and it's too big. Really high, and where the chip is - it can hit your video card ... and that's never good. I uninstalled one of them and replaced it with the vizo one. It's been running about a year or two, and has worked nicely.
The chipset cooler is probably clipped in with 2 plastic pins. Get a needlenose or other small pilers - and squeeze the pin from under the board ( it's like an expanding arrow lock thing. The pin usually looks like this:
http://ep.yimg.com/ca/I/yhst-50621372921554_2096_6676915 - white plastic pin right in the foreground of the picture. ) See if you can pull it out from the top of the board once you have it squeezed. If you can't, just twist off the bottom real carefully ( don't scratch or touch the board ) from the bottom - while holding the top still --- OR --- you can snap off the top where it holds the pin down. Either way should work to break it off. They're pretty weak, so it can just break right off. If it has thermal tape on it, you'll want to slowly work it off by twisting it side-to-side. It may have a paste under it as well ... that may be very rigid due to being old. Same thing as the thermal tape - just work it slow & easy, it'll wear out. Don't try lifting it - if secured - until you feel it's good and loose.
The new fan should have installation instructions on how to secure it and all that. Make sure the pins are the right distance before you pull off the old one.