Yum is a standard installation utility for CentOS 5.2. One of the reasons I favor CentOS over other Linux distros is actually because it comes with yum. It is that good!
Unfortunately, CentOS 5.2 does not generally include the latest versions of libraries, because it follows conservative path of the RedHat Enterprise. Which is not that bad of an idea, for a server OS... until you need that latest version of something and you are stuck... or: not necessarily.
If you a are a Drupal developer, there's a very good reason why you need the latest version of PHP: 5.2. The reason is called FileField module. This module is required by another absolutely essential module ImageField making it a matter of life-or-death (just kidding) to have PHP 5.2 on your server. But the latest CentOS release (ironically also 5.2) only comes with PHP 5.1.6.
What to do?