Meszaros Marton and other PHP coders have started a Test-Driven Development project centered on showing the methodology to new adopters in a green field. The goal of the project, named Munchkin, is creating a feed aggregator - like Google Reader - from scratch. The authors will post a series of articles about their development process along the way. If you want to follow a step-by-step guide to implementing an Agile project with TDD in PHP, follow them.
Their goal is to show you not only how TDD can make your application better but detailed tutorials on setting up your environment and making effective use of the tools in an agile environment.