You could mount a cpu fan onto the card somehow. But what you should really do is look into some aftermarket fans/coolers made for the radeon 9800. There's a large selection available Here
Just look for one that fits your budget, and that lists the radeon 9800 as compatible. I'm not an expert on VGA cooling by any means, but you should be able to take any of these generic fans and attach it to the card, or replace the heatsink.
Well, if you have a 9800, you're computer is clearly not up to date by any means. So, if something breaks it's just more incentive to build a new one. I'm not saying that's what should have to do, but it's an option. If you don't want to do that than either get a new card or fan.
Ummm...I'd more concerned for the reason that if your fan died, maybe your GPU might be fried?? If the card was running with a fan that wasn't working, the chip may be heat damaged...I think a new card would save a lot of headache if you need the computer anytime soon....
Hell, if the computer still works, why not spend $10 to get a perfectly (assuming GPU isnt fried) good computer working. Even if its not up to date, someone has a use for it. Sure, it sucks on modern games, but for general use, itll be adequate, or slightly slow for video editing.
For video editing, it might be worth your while to update your rig, the processor is certainly much worse than a modern system.