From blogs.msdn.com:

The Dream.Build.Play Challenge is back, and we’re more excited than ever to see your ideas come to life. Build the next mind-blowing game for Xbox 360® by using XNA Game Studio 4.0, and you could win! Winning game developers split $75,000 USD in prizes and get a shot at an Xbox LIVE® Arcade publishing contract, and their games will be featured on Xbox LIVE Marketplace. Set the power of your imagination free – and let the game challenge begin!

Registration: Feb 28 – May 17
Game Submission: May 17 – June 14

See Dream.Build.Play for details and to register.