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EPEL is a community-driven, Redhat-backed repository for use with Enterprise Linux (and therefore CentOS, Rocks, etc). It provides many useful packages not provided by the official repositories while maintaining compatibility with upstream releases.
See more: https://fedoraproject.org/wiki/EPEL
Install the EPEL RPM directly from the repository, which will add support in your system's yum.
$ rpm -i http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm