The Extra Packages for Enterprise Linux (or EPEL) can be installed on any CentOS 4, CentOS 5 or CentOS 6 server using the following commands:
CentOS 4
# rpm -Uvh http://download.fedora.redhat.com/pub/epel/4/i386/epel-release-4-10.noarch.rpm
CentOS 5
# rpm -Uvh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-4.noarch.rpm
CentOS 6
# rpm -Uvh http://download.fedora.redhat.com/pub/epel/6/i386/epel-release-6-5.noarch.rpm
Once you have completed the installation you can install packages from EPEL using:
# yum install package-name