Mocking libraries are great; however, some require additional requirements to use this library.  With installing TypeMock or TestDriven.NET, TypeMock will work when unit testing with in Visual Studio, by setting the startup program to the NUnit application.  However, running NUnit independently requires that some startup functions occur via script, which these instructions are available on the web site.  There is a Visual Studio Add-In that TypeMock uses, which is why you do not need to configure anything when running the project in the editor.  For running instructions, view the TypeMock web site.