In this new post from Derick Rethans today, he explains how to run PHP 4.3 and PHP 4.4 concurrently via this HOWTO.

As I wrote before, PHP 4.4 addresses a couple of very serious memory corruption problems when dealing with references. Previously you had to work around these problems. But with the workarounds in place you will now see that things no longer with with PHP 4.4. This is a real problem if you have a large application (like eZ publish) as you know might need to run PHP 4.4 for the sites with an upgraded eZ publish, but also PHP 4.3 for the non-upgraded sites. Because of this I wrote a little HOWTO with information how you can set this up.

The HOWTO lays it out simply, giving command line examples, httpd.conf directives, and even an /etc/hosts setting to ensure that it will all work via one IP. He makes it look so easy...