It's a bit of a pain that many basic third party tools that aren't put of the main Centos/RHEL repositories are not available unless you compile them or install the RPMForge Repo.
*Updated 08/29 with new download location changed from apt.sw.be to rpmforge.sw.be
Here's a quick, simple/cut&paste way to do it:
wget http://rpmforge.sw.be/redhat/el5/en/i386/rpmforge/RPMS/rpmforge-release-0.5.1-1.el5.rf.i386.rpm
rpm -i rpmforge........