The below will show you how to add the Dag Wieers repository to Centos 5.3 I have also used this method for lower versions of Centos as well.
First you need to run this code from the console or via putty.
In order to add this repository to your yum configuration for any version of RHEL, create the file /etc/yum.repos.d/dag.repo containing
name=Dag RPM Repository for Red Hat Enterprise Linux
You should now be able to use the Dag Wieers repository using YUM