what i did when i had to do this in school was have somebody dance infront of the greenscreen, and layed 2 tracks down in premiere. I then greenscreened the first one, so the person dancing was all that was there, then i did an inverse mask on the other so the first one was the bg, then the second one was a black sillouete (spelling) of the person.... worked seamlessly
Mac G5 workstation with 4 gigs of ram, 4x250 gig drives in raid 5. High availability cluster server running centos for a server. 2xCanon GL2 cameras.