Ben Ramsey has a new post to his blog today on how to get a development version of the PHP integration into Appcelerator working until they get everything up and merged with the main branch.

If you’re not familiar with Titanium, it’s a development platform that allows you to build native desktop applications for Windows, Mac OS X, and Linux using the Web technologies we use on a daily basis: HTML, JavaScript, CSS, Python, Ruby, and now PHP. [...] Since it may still be a while before the next release of Titanium that includes PHP, I’ve decided to provide instructions here on how to build the SDK from the master branch and connect it to the Titanium Developer application

You'll need to download and install the latest developer tool from the Appcelerator site, a package with the development SDK in it. Change a few links around, add some symlinks and you should be all set.