On the SitePoint.com Web Tech blog, Craig Buckler explains how you can test multiple PHP/MySQL/Apache websites on your local machine without having to change your Apache configuration each time - the magic of VirtualHosts.
It is rare to find a web developer with responsibility for just one website. In this article, we will configure your development PC so you can test any number of websites using a dedicated domain name for each one. You will require a local installation of Apache 2.2 and, optionally, PHP and MySQL.
He explains the only two parts you'll need to get it up and running - changes to your hosts file and updates to the Apache configuration file to add in VirtualHost records for each site. He also throws in a bonus tip about detecting which host the script is being used on via the $_SERVER['HTTP_HOST'] variable.