Short attention span? No problem. Hilary Pike has created a short quick moving demo/screen cast on modifying an existing 2-dimensional XNA based video game. In just 10 minutes she walks the viewer through some key gaming concepts and then adds Collision Detection and Score Keeping to the game.
Also at her blog post you will find links to other XNA resources and of course the sample code for the game used in the demo. This demo will give a good overview of what one can do with existing game code for XNA projects. And of course collision detection and score keeping are important things for just about any good computer game. Share it with your friends.