Andrew Podner has a posted the second part of his series looking at functional testing in PHP applications with Selenum.

In the first post about functional testing, we went through the basics of what functional testing is and how it complements and differs from other types of testing used for software quality assurance. This time, I will spend some time talking about using functional testing in a practical sense to set up a testing suite for a web based software project. [...] Each of these can provide a powerful means of performing automated functional testing and you should select your tool of choice based on what works best for you. I typically find myself using Selenium for functional testing, but again, I would encourage you to look at each available option out there and select the best fit

He walks you through the installation of the Selenium Firefox plugin, some of the basics of its use and how to create and run a simple test. He also looks at a slightly more complex example - filling in a form and validating the resulting page.