The folks over at Dream, Build, Play have posted details on the first part of their contest. In what they are calling the 'Warmup Challenge - Relatives of Spacewar', the goal is to create a game based on the SpaceWar Starter Kit. From the "How to Play" page:
Create a game based on the Spacewar Starter Kit... either the Spacewar codebase or content, or both. The only requirement: Your game must be derived from the version of Spacewar that's a part of XNA Game Studio Express. Use as much or as little of the Spacewar Starter Kit as you like. Just remember that the relationship to the Spacewar Starter Kit must be obvious to our judges.
The five best entries will each receive a prize of $500, but you need to act fast, as the deadline for submitting your game is Feb 28, 2007!