You could download the source package from http://www.erlang.org/download.html, then follow the README in the package and install. You will need at least these packages: ncurses-devel, openssl-devel, unixODBC, java-1.xx-openjdk-devel.

Or, you could use the pre-packaged ones. On CentOS 5, you can install the fedora repos, and then yum install the Erlang from there:

# rpm -Uvh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarc...

and then install erlang and all it's dependencies on CentOS by typing "yum install erlang".