To use our update service with yum copy the *.repo files you need from here to your local /etc/yum.repos.d/ catalog and run yum clean all and yum update.
We currently support CentOS 4 and 5 and Fedora 6 (5 is expired from the Fedora Team support and should not be used)
We mirror a lot of repos from different sources, mix them with care, our experience is that rpmforge and kde-redhat works well together with CentOS, livna and kde-redhat works well together with Fedora. We are not saying that other combinations will not work, but the aforementioned repos are the ones we primarily use.
Send comments and suggestions to me.