Today at Microsoft’s press conference during E3 2007 Peter Moore (Microsoft) and the developers from Harmonix treated everyone to a Demo of Rock Band.

Rock Band is a music video game under development by Harmonix Music Systems, published by MTV Games, and to be distributed by Electronic Arts Partners scheduled to be released during the fall of 2007.

Developed for the PlayStation 3 and Xbox 360, Rock Band will offer players the ability to function in a virtual band by providing up to 4 players with the ability to utilize three different instrument-based peripherals (a guitar peripheral for guitar and bass/rhythm guitar sequences, a drum peripheral, and a microphone) and allowing them to interact through both online and offline multiplayer capabilities.

You can see some screenshots of the game and pictures of the peripherals at IGN.com

You can also see video of the game in action and the E3 demo here.