To do so you have to download the Community Game Blade, to do so you must go here:
Marketplace blade > New Arrivals > Game Content > XNA Creators Club > XNA Creators Club Game Launcher (7mb)
Download it and a new Blade will appear, allowing you to download demos of these games:

• “JellyCar.” Created by Walaber from the United States, this game is about driving a squishy car through squishy worlds, trying to reach the exit.
Click here for more images of Jelly / Jello Car!

• “Little Gamers.” This is a 2-D high definition action side-scroller based on the famous Web comic “Little Gamers” created by Loïc Dansart, a 24-year-old software developer from Belgium.
Click here for more images of Little Gamers!

• “The Dishwasher: Dead Samurai.” An intense 2-D action platform game created by James Silva from the United States, “The Dishwasher: Dead Samurai” has a unique, highly stylized look and fast and fluid action.
Click here for more images of The Dishwasher!

• “TriLinea.” This puzzle game created by Edison S. Prata Jr., Renato Pelizzari da Silva and Davi da Silva Prata from Brazil mixes fast-paced action with strategy.
Click here for more images of TriLinea!

• “RocketBall.” Created by Tyler Wanlass, Patrick Murty and Todd Barrons of the United States, this neighborhood game of dodgeball explodes onto the street with fast-paced multiplayer action.
Click here for more images of RocketBall!

• “ProximityHD.” This game, created by Brian Cable from the United States, takes the essence of strategy games — battles for control of territory and armies — and distills it down to a simple, easy-to-understand set of rules for casual players.
Click here for more images of Proximity HD!

• “Culture.” Created by independent game development company Hidden Path Entertainment from the United States, “Culture” contains challenging games and puzzles based on beautiful flowers.
Click here for more images of Culture!