Although Drupals 7+ run smoothly on PHP 5.3, Drupal 6 still feels much better with PHP 5.2. Even though D6 core is compatible with PHP 5.3 for quite some time now, a lot of contributes modules still get nasty hiccup when asked to run on the newer version. Therefore developing for both D7 and D6 at the same time becomes much less painful when running both versions of PHP in parallel.
One way of doing it is using mod_php5 Apache module to serve PHP 5.3 applications, while running PHP 5.2 applications using fastcgi module. Under Ubuntu 12.04 this can be achieved by installing PHP 5.3 from the repositories and manually compiling and installing PHP 5.2 afterwards. Читать далее