Compositing/Rotoscoping tools
 

What software would be best for say, having a green screen hand, and removing it and replacing it with some cg and make it look like it actually fits the scene?

Maybe I'm jumping in the deep end here, but if those guys at ILM can do it then so can I! :)

I use 3DStudio for modeling and Adobe After Effects for the compositing (both PC based). Your needs may vary, but this seems to work for everything I've ever done.

Tom

There are a lot of packages out now-a-days to do this kind of
things. Most serious NLE (Non Linear Editors) have at least
basic support for this as well (including Premiere and Vegas).

Other packages that come to mind are After Effects and
Combustion.