first, and you probably wont really ever need this unless you're doing a bare bones install of a cent/rhel box, the webtactic repo maintains a decently up to date git install that will cleaning go onto such a box:
sudo rpm -Uvh http://repo.webtatic.com/yum/centos/5/latest.rpm
sudo yum install --enablerepo=webtatic git-all
Now you have working git!