I won't bore everyone with 30 days of my quest to understanding Test Driven Development and Unit Testing, but I ran across additional resources the past 2 days that I think are worth reading and listening to if you are interested in knowing more about it.
First, the most recent .NET Rocks Show, June 14, 2004, has guests John Alexander and Berry Gervin who talk about NUnit, Test Driven Development, and Extreme Programming. It gives a great overview on these concepts as well as their own experiences.
Second, the Code Project has an article, called Advanced Unit Testing, Part I - Overview, by Marc Clifton that also talks about NUnit, Test Driven Development, and Extreme Programming. This is definitely worth reading to understand the origins of Test Driven Development. Marc actually writes 5 parts in this series, but parts 2, 3, 4, and 5 are building a replacement to NUnit. Those parts are for the hardcore developers, whereas Part I is great for just understanding the methodologies and NUnit.
I feel I should mention that just because I am attempting to understand Test Driven Development and Extreme Programming along with Unit Testing, I am not advocating or promoting these methodologies. My main goal is to understand NUnit forwards and backwards and my knowledge wouldn't be complete without understanding NUnit's origins and uses in the industry. I am still coming up with my own conclusions on TDD and XP.