Ladislav Prskavec has posted a step-by-step guide on getting Hudson (a Java-based continuous integration server) working with PHP.

Hudson is extensible continuous integration engine used for Java projects. It’s architecture can be used for others languages as PHP too.

The guide links you to the files and packages you'll need to get PHP support installed (including a few different plugins), a sample build script for a build tool like Phing and an example Hudson configuration to tie them together. The Phing process is executed in a shell to run unit tests, build documentation and check the syntax on all files in the current repository.