I was beginning to wonder if TDD would ever make it into mainstream development in Sri Lanka, but looks like it’s slowly happening. The following is my reply to a post on the .NET Forum

Based on my understanding so far unit testing works best for testing the Business Logic of your system. And the de facto tool for unit testing in .NET is nUnit. The most effective way to test your application using nUnit is to use a development methodology known as TDD. The following links should help you out.

nUnit - http://nunit.org/
'The' Book - Test Driven Development in Microsoft .NET
'The' Site - http://www.testdriven.com

 Questions that I had when starting out on unit testing.
How do I unit test the UI?
Practically I don't think it will be feasible to unit test the UI layer in an enterprise level application, but if your interested try these.
http://nunitforms.sourceforge.net/
http://nunitasp.sourceforge.net/

How do I unit test the Data Access Layer?
Here too I don't think you would really gain much from unit testing since you would pretty much be testing the database, network connections, etc. But I did find this article that can show you a way to do it.
MSDN: Unit Test Your .NET Data Access Layer

On the other hand you could also take a look at the NMock framework that allows you to mock objects that are resource intensive, etc. http://www.nmock.org/

Hope this helps.