I'm intrigued. I've got an nVidia 460 GTX, I'll see how well that works...

Edit: A calculator I came across (http://www.alloscomp.com/bitcoin/calculator.php) says that I should be able to generate just over 3 BTC a month, or about 50-55 USD. And that is, I'm assuming, if I leave it mining 24/7, which I don't intend to do.

The client is still downloading blocks, but it should be done soon. I'll leave it on overnight and see what happens.