Any 8000 series Nvidia card is probably overkill, since the only real advantage they have over the 7000 series is DirectX 10 support. If one isn't running Vista, it's pretty much pointless as the 7000 series is generally cheaper. Easiest bet is really just to surf through a joint like Newegg and take a look at the graphics cards in that area that don't use fans. For example, here's one for $57.

http://www.newegg.com/Product/Produc...82E16814121021

Of course, I don't know the particular specs of your machine, but if you look around this section here, you can probably find something silent, affordable, and practical if not more than what you need. And, of course, read the user reviews.

http://www.newegg.com/Product/Produc...82E16814121064