php 5.2 and additional repos

I am new the RHEL 5.  We subscribed because we don't have any
dedicated system admins and wanted to make administration of our
servers as easy as possible.  But RHEL doesn't have everything we
need.  In particular, I am very surprised that it doesn't include php
5.2, which many php apps are starting to require.

What is the easiest way to install software like php 5.2 on RHEL 5
without updating virtually all of the system software?  Can I just add
a repository for yum, like maybe Fedora 10 (or perhaps an older
version like 9 is more compatible with RHEL 5 core)?  Or should it be
a repo of sw built specifically for RHEL5?  If so, are there any?

thanks for any advice offered,
-Don