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Originally posted by M. Krass
Lock the camera. If the camera is stationary, it'll be far easier for you to put in animation that appears to fit. If the camera moves and the lighting and perspective changes, animated things will look very, very bad unless you're an utterly incredible animator.

Incredible animator? More like a person who knows how to use Post-Production Programs.
I know that in After Effects you can create a synthetic light to match the one in the Animation. (Keyframing or tracking)
And you can create a primative (Biped) in 3ds, Maya, XSI etc. and match it's movements to the one in video so it will have shadows on sufaces to correspond w/ the position of the live-action character.
It's Not that hard when you have programs to track the motion instead of you:
Maya Live (In Maya Unlimited)
Match Mover
etc...