Import the Centos GPG Key

rpm --import  /usr/share/doc/centos-release-4/RPM-GPG-KEY

Install the Dag repository

rpm --import http://dag.wieers.com/packages/RPM-GPG-KEY.dag.txt

# cat <<EOF > /etc/yum.repos.d/dag.repo
[dag]
name=Dag RPM Repository for Red Hat Enterprise Linux
baseurl=http://apt.sw.be/redhat/el\$releasever/en/\$basearch/dag
gpgcheck=1
enabled=1
EOF