I had that same problem way back.
I used to have a VIsiontek Geforce 4 Ti4600... damn fan was starting to go bad, so I replaced it with this heatsink kit http://www.extremeoverclocking.com/r...CoolMOD_1.html
To remove the old heatsink, you gotta use your card and let it get hot, ( run a 3d game for 20-30 Min. depending. If your fan is not even moving, then this option may not be for you.) this will loosen the yellowish thermal material that has bonded to the chip. Remove the video card, pop the pins and then gently twist the stock cooler clockwise and counter clockwise and it should eventually pop off.