On the ServerGrove blog today there's a new post from Ishmael about setting up multiple versions of PHP on one Apache instance with the help of FastCGI.

There are several reasons you might need to run multiple versions of PHP on the same server. Maybe you have a PHP 5.2 application running on your server and you need to start working on another application based on a new framework like Symfony2 or Lithium? Perhaps you haver a client with a legacy site that runs PHP 5.2, or maybe you simply want to test some of the new functionality? This post is going to explain how to setup a server to run multiple versions of PHP.

Normally, Apache can only be compiled with one version of PHP, but FastCGI gets around that by letting you define it in a configuration file instead. They also include support for defining the user the process runs as (suexec) that helps to make permissions issues lesser. Included are all of the command-line calls and config settings you'll need to make to get things set up.