When you update the RHN, there should have been 3 rpm's. Due to circular dependancies, they all need to be installed at the same time. I think the command is rpm -ivh up2date*.rpm. The * is a "wild card". This tells RH to install any and all rpm's starting with "up2date".
It's been a while since I did this but I found this on the RHN page. The README files say it all, even though sometimes you have to dig pretty deep.