Well, I have just upgraded my Bluequartz CentOS server to PHP5 while retaining PHP4 for the BQ Admin Server.

You don’t need to spend money on a Package that does what you can do for free. I followed the HowTo at http://www.osoffice.co.uk/forum/viewtopic.php?f=12&t=368 and it appears to be working very well.

As a bonus It upgraded Apache, MySQL and PostgreSQL and Perl along with PHP5 but retaining PHP4 for the admin section.