Not much. The THEATRE 200 chip has an additional 5% MPEG hardware load. THEATRE chipsets encode video with a "hybrid" method, using both hardware and software in tandem. The 200 chips are the new ones. The 100 chips were also called RAGE THEATRE chips.
All THEATRE chips from the RADEON-class AIW line-up are pretty much the same, in terms of output quality and how they act. The native resolution of the 200 is also a few pixels different from the 100, but both are very close to 704x480 native.