Michael Girouard has posted a new guide today about getting PHP 5.2.9 up and running on a CentOS distribution:
CentOS in my opinion is the best way to go in terms of server distros. Some people, including myself, are frustrated at the fact that some software is slow to be updated out of a fresh install: specifically PHP. At the time of this writing, PHP 5.1.6 is the version shipped with CentOS 5.4. While I’m sure they have their reasons for this, I still am required to write somewhat modern apps — 5.1 just doesn’t cut it anymore.
He suggests moving away from the compile from source option and "go with the flow" and work with the packages that've already been created. You have to get the testing repository set up first (creating a configuration file to add the name, baseurl and other keys) to be able to use the yum installer tool to grab the latest packages.