Runs Great on my iMac 20" with the 2gig PPC Processor. running Leopard
I can be converting Movies on the Mac, downloading new movies, and surfing the web, all while the G/F is streaming Movies from Itunes to the Apple TV,
The biggest requirement is your wireless connection, I replaced my DLINK Wireless router with an Apple Air Port Extreme, and streaming is no longer an issues (Noticed with the DLink that the stream would sometimes shudder)