Just found it - will watch now. For anyone else who's interested:
http://www.youtube.com/watch?v=53jzv3ztOLY
EDIT - just watched the footage. Yeah, you're spot on Cantanky, Bowie was TOTALLY wired on coke on the Cavett show - sniffy, twitchy, jerking, fiddling with his cane, making eye contact with random things/people continually...the "Cracked Actor" footage of Bowie in car is far more restrained and relaxed...