unread
Shameless plug: I just posted a beginner's tutorial on my own
multiple-php-installs setup:
http://gggeek.altervista.org/2007/07/21/running-multiple-php-versions-on-a-single-apache-install/
it contains links to many similar blog posts that a quick Google search
returned.
The most complete one is:
http://www.gentoo.org/proj/en/php/php4-php5-configuration.xml
Gaetano