UPDATE - more confimation
Xbox360Fanboy.com is reporting that the Prey demo will be out on June 22, 2006(Thursday).
In Prey, players enter a living spaceship which enslaves alien races and devours humans for lunch. A unique twist on the first person shooter genre, Prey features such innovations as the ability to walk on walls, manipulate gravity and perform a "spirit walk" by leaving your physical body behind. Designed by Human Head and brought to Xbox 360 by Venom Games (under the direction of 3D Realms), Prey features full online support for up to eight players, utilizing the game's play innovations for unique multiplayer experiences.