1. what distro are you using?
2. are you using YUM or apt?
if its apt, then you need to edit your sources.list as root, if you are using YUM, then you need to edit your yum.conf as root.
in either case you need to run update of what ever package manager you are using.
if you are running MDK, then why would you be pointing to a RH list? i know nothing about MDK other then it is an other rpm based distro, but i would only guess that MDK has their own set of respoitories as the RPMs for RH/FC are different then those for MDK