It should work with it. Your power supply should be sufficient, but don't expect to be able to play current games above low settings. You'll be able to hit medium on some undemanding titles assuming your at 1280x1024 or lower resolution.
eta: if you state your price range somebody can probably recommend a better card than the 8600gt.
eeta: he has a PCI-E slot, but only 305W on his PSU.
I play on 1024x768, and all I would play is MMO's, some FPS.
And by the looks of it, it can play modern games at playable FPS. (Watched some youtube vids of gameplay with it)
And yeah 305W is enough. (18A on the +12v rails)