for what you'll pay for a decent fan (the link posted) plus tax and shipping ($40)
and what you can sell the 9800pro for ($60 assuming it's not AIW)
and $30 more
you can get a newer generation card (6800xt or x800 gto or x800xl refurbed) that will run MUCH faster than the once king 9800pro from almost 4 years ago.
But if you're dead set on keeping your 9800 (I still have my 9800 pro AIW), then more power to you.