I was very pleased with the two-part article "Test Driven Development in Python" on O'Reilly's site:
http://www.onlamp.com/pub/a/python/2004/12/02/tdd_pyunit.html - waybackmachine
http://www.onlamp.com/pub/a/python/2005/02/03/tdd_pyunit2.html - waybackmachine 2/3 and 3/3
These really cleared up how to use Python's unittest module for TDD, as well as giving me a good dose of the TDD mindset.