(required in order to get many many other useful things)
sudo rpm -Uvh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-4.noarch.rpm
sudo yum install git
that link will change depending on your version of CentOS, and of course it changes over time. Look it up at https://fedoraproject.org/wiki/EPEL