http://www.codeplex.com/raycasterx
RaycasterX is an MIT-licensed project geared towards the creation of a full raycasting engine for XNA. Currently RaycasterX is built against the XNA Game Studio 3.0
CTP providing support on both Windows and Zune. Xbox 360 support will be added when a version of XNA Game Studio 3.0 is released that supports Xbox 360 building and deployment.
RaycasterX is primarily based on the tutorials of Lode Vandevenne found here:
http://student.kuleuven.be/~m0216922/CG/. Some changes and extensions have been added both for ease of use and the transition from C++ to C#.
This is the base engine I used for my ZuneShooter WIP. I have decided to stop working on that project for a couple reasons:
1) Performance on the Zune just couldn't keep up and I'm too pre-occupied with DreamBuildPlay (
http://dreambuildplay.com/main/default.aspx) to spend much time with it.
2) It really isn't that fun.

Controls on the Zune just aren't fun for playing a first person shooter.
However if you disagree, here's the full raycasting rendering code you need to start putting a shooter (or RPG or racing game or whatever) together. Have fun!