On the Server-Side Magazine site there's a recent post for the cutting edge developers out there that want to get to testing their code on PHP 5.3 but don't want to cause issues with their current environment. The solution? Install Ubuntu in a VirutalBox instance!
Since the official release of PHP 5.3 many developers want to test the new features out, but still don’t want to mess with the old PHP installation. Same thing goes for me, I don’t want to mess up my existing PHP installation yet, but eager to test namespaces, late static binding and closures. So let's create a virtual development environment using the latest software bundles.
They walk you through every step of the way - complete with screenshots - to get Apache 2, MySQL 5 and PHP all up and running inside of a VirtualBox running Ubuntu 9.04. You'll need to know a little bit about working with packages and compiling to get the job done (there's no official PHP 5.3 package yet) and be able to use your editor of choice to change a few values in configuration files.