Yes, the cat is out of the bag now ... you can win all of the above-mentioned prizes if you "... push the limits of Artificial Intelligence while building a game with XNA Game Studio 2.0 ...".
Interested? Then head over the Dream.Build.Play site, read the rules, dates, prizes and start coding! Hurry up! The entry period for submissions starts on December 20, 2007 and ends on January 27, 2008.
Cheers![Well Ziggy, one part of the plot is known, so I guess we'll now have to wait for a soon release of XNA GS v2 final ...]