If you are looking for a good high level introduction to TDD in .NET then I recommend you walk through the example from Chapter 2 of Test-Driven Development in Microsoft .NET. In this example you will also get a feel for how NUnit fits into The Picture. If That Does Not Wanting More The Stay Tuned for An Updated Real Work Example from James Newkirk (One of the Authors for this Book).
I think i am officially hooked to tdd ... time to buy!
