Look here. According to the Major:
Download the XNA Creators Club Game Launcher in order to play the special preview selection of game demos created by the community using XNA Game Studio. When your download is complete, go to the Games Library, select My Games, and navigate to the XNA Creators Club category along the top. From there, press Y to view, download, and play the available trial games for this limited period.
Limited period. Not so good. Take advantage of it, quick.