k....
you don't have to key the footage from the greenscreen until after you've gotten your render from maya - in fact, depending on how things are setup, keeping the full frame may be better. The basic idea is that you take your accumulated video footage (usually on a shot-by-shot basis), strip it out to frames (usually as a .jpeg file) and then import it into maya. Then you animate or whatever else needs doing, render out the stuff in maya (minus whatever footage you shot), and import that into after effects (or whatever program you have), which you then use to composite the footage (this is the point at which you key the computer for the background). At least, that's the way I'd do it...

I have maya 6.5 as well. That's not what you need to look for. If you look in the drop-down menu (which contains modeling, animation, dynamics, etc) Live should be in there, if you have it and the plugin is enabled. You'd also be able to tell whether you have Unlimited or Complete by the name on the shortcuts that maya gives you (ie. "Maya Unlimited 6.5", etc).