Usual opensource mocking frameworks can mock only interfaces and virtual methods. In contrary to that, Microsoft Moles can ‘mock’ virtually anything. Here's a little overview over this framework, together with a suitable Gallio extension...
This post started out to be a reply to another blog post about some detail of the red/green/refactor cycle in TDD. It ended up as a fairly extensive description of my own personal practice of doing TDD in C#, featuring quite some VS add-ins and discussing some (real-world) aspects of test-driven development along the way...