It’s very easy, using CentOS own Repositories & the ‘yum’ package management system to install a version of PHP 5.2 to CentOS 5.6
First, configure your yum to use the official CentOS 5 “Testing” Repo, by creating the file /etc/yum.repos.d/CentOS-Test.repo
containing the following:
[c5-testing]
name=CentOS-5 Testing
baseurl=http://dev.centos.org/centos/5/testing/$basearch/
enabled=1
gpgcheck=1
gpgkey=http://dev.centos.org/centos/RPM-GPG-KEY-CentOS-testing
Then (as root) run ‘yum upgrade php
‘ & you’re done!