I was a little scared when it came to setting up Selenium, I figured it was going to be difficult to setup and configure. So I was pleasantly surprised when it really wasn't. So here are a few of the mistakes I made; since I use Vagrant to do all my development I actually grabbed Selenium and started from there. Not a good place to start, although as I found out later; not a total dead end.
He includes the initial setup of things like PHPUnit and the Selenium .jar file as well as a sample test that loads a page and checks the title of the page. His second post shows how to set it up in the VM (using Vagrant, xvfb to capture the output and Firefox to execute the tests).