LiveView with chroma-key from camera, to pc, to TV

[borfast]

Hi everyone!

I'm looking for a camera that allows me to connect it to a PC, point it to a scene with a green background, and have the PC show it on a TV, overlaid on a second image, replacing the green background with the second image.

Basically, I'm talking about real-time/live chroma-key/green-screen from the camera, to the PC, to the TV.

I've been looking at the Nikon D90, since it's cheap and has the Live View feature I'm looking for. Can anyone confirm if it's capable of doing what I described above?
What other cheap cameras would work for this?
I prefer Nikon just because I have a couple of Nikkor lenses from my D40x and would prefer to avoid having to buy new lenses for a Canon camera, but if the price justifies it, I'll change.

Software suggestions are also welcome, although I doubt a lot of people will be able to help me here, since I need software for Linux, not Windows or Mac. Windows suggestions might still be valuable, though, if I can run the software on Wine.

Thanks!

Edit: Just to clarify, my goal is to have the LiveView "feed" from the camera to the PC, where the chroma-keying occurs, and is then output to the TV.