Does any body know a command and conquer game which is open source? I would like to experiment with writing AI's for a command and conquer game. I am not overly interested in having to code the units etc from scratch, I simply want to test a few theories, but if there's room to grow that would be great. I currently have a windows system. I am an experienced C#/database developer aka a Web developer. Furthermore if there is some book that would adequately teach game programming that would be great. I have also been doing some reading of managed C++ and will probably do some reading on marshaling dll's.

I don't know anything about CnC, but there's an API for StarCraft that can be used to write AIs. There are wrappers for multiple languages etc. Fairly easy to work with IIRC, not sure about debugging etc though.

Oh thank God Happy Coder! This could be cool. If more come up please let me know, I would love to vet the ones that are closest to my jonra. 

Of the ones on Happy Coder's list, OpenRA should be the closest to what you are looking for: it was made for classic Command and Conquer games.