If, like me, you're slowly getting into test-driven development, it becomes apparent that there are several ways to create a class library and a set of tests that challenge it in Visual Studio. Then it becomes obvious that the best way to do it and not leave test code in your releases is to create something like this where the tests are in a separate project.
To speed up the creation of solutions like these, I've created two templates to plug into Visual Studio to do it for you. There's one for testing with MbUnit 2.3 RTM and one for NUnit2.2.9. Download the one you want to your VS2005 Project Templates folder and then create a new project. You'll see the options to use the templates automagically.
Let me know how you get on and if you'd change them in some way.