Before I start, please let me say that I am a Microsoft Developer and quite often, evangelist. I enjoy working with C# .NET, and find that it is an efficient and economical choice for many projects - not all, obviously.
I also support and strongly recommend Test-Driven-Development and Continuous Integration.
By far and wide the best tool I have found for this is TestDriven.NET. However, Microsoft have some issues with the fact that this plugin can be used with VS2005 Express, and haven't been entirely fair with the developer - they have - rather than explaining what they want him to do - simply released the evil flying monkies. Err. I mean lawyers.
See here for more info (the authors blog). If you don't already use TestDriven.NET, you may want to.