Since ISPConfig 3.0.5, it is possible to use multiple PHP versions on one server and select the optimal PHP version for a website. If you have some very old websites on your server, they might not work with PHP5, but only with PHP4. This tutorial shows how to build PHP 4.4.9 as a FastCGI version for use with Apache2 on a Debian Wheezy server. This PHP version can be used together with the default PHP (installed through apt) in ISPConfig.