Estimado co2pd e configurado deacuerdo a tu manual dag, aunque tengo el siguiente error al momento de tratar de actualizar o descargar informacion con yum:

[root@servicios yum.repos.d]# yum update xmms
Setting up Update Process
Setting up repositories
http://apt.sw.be/redhat/4/en/i386/dag/repodata/repomd.xml: [Errno 4] IOError: HTTP Error 404: Not Found
Trying other mirror.
Cannot open/read repomd.xml file for repository: dag
failure: repodata/repomd.xml from dag: [Errno 256] No more mirrors to try.
Error: failure: repodata/repomd.xml from dag: [Errno 256] No more mirrors to try.
[root@servicios yum.repos.d]#

===========================================================

Pues e configurado el repositorio de la siguiente manera:
[root@servicios yum.repos.d]# ls
CentOS-Base.repo dag.repo
[root@servicios yum.repos.d]# vi 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

[dag]
name=Dag RPM Repository for Fedora Core
baseurl=http://apt.sw.be/fedora/$releasever/en/$basearch/dag
gpgcheck=1
enabled=1

[dag]
name=Dag RPM Repository for older Red Hat Linux
baseurl=http://apt.sw.be/redhat/$releasever/en/$basearch/dag
gpgcheck=1
enabled=1

=================================================================

De igual manera le e dejado el repositorio de centos que viene preeinstalado:
[root@servicios yum.repos.d]# vi CentOS-Base.repo
name=CentOS-$releasever - Extras
baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4

#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4

#packages in testing
[testing]
name=CentOS-$releasever - Testing
baseurl=http://mirror.centos.org/centos/$releasever/testing/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
"CentOS-Base.repo" 50L, 1554C 50,1 Final

================================================================

mi archivo yum.conf esta de la siguiente manera:
[root@servicios etc]# vi yum.conf

[main]
cachedir=/var/cache/yum
debuglevel=2
logfile=/var/log/yum.log
pkgpolicy=newest
distroverpkg=centos-release
tolerant=1
exactarch=1
retries=20
obsoletes=1
gpgcheck=1

# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d

saludos...............