Those hoping that Unreal Tournament 3 would be getting the Crackdown treatment by including a multiplayer beta/demo for Gears of War 2 will be disappointed to learn that there are no plans to release a demo of the game.  Gears of War 2 associate producer Tanya Jessen has recently stated that the relatively short production time for a game of this caliber, two years, and that fact they they're focusing on putting out the best possible game, means they do not want to divert any resources into making what amounts to a second product, a demo.

source: http://www.shacknews.com/onearticle.x/52306

Check this out http://www.gamepro.com/microsoft/xbox360/games/features/178290.shtml

Great Gears of War 2 article from Gamepro

That kind of sucks, but since this games has guaranteed high sales a demo isn't really necessary. The Halo one wasn't needed either, but they were going for total media saturation leading up to the release.

Demos are like fittings room at a clothes store - you get to try on an outfit, and if you don't like it just put it back. I demoed Lost Planet and didn't like how the controls felt so it went from a "might buy" to a "won't buy." Conversely, I played the demo for Psychonauts on Steam, and am now planning on getting it form xbox originals.