I'm not too familair with MDK 10, but I know mdk 9 still had rpm as well as urpm. I would assume it still has both. Try rpm -ivh kernel-source-2.6.3-7mdk.rpm or urpm -ivh. Post the exact error message here. It could be a dependency problem. You might also want to try putting the full path to the file ie.
rpm -ivh /home/user/mycooldownloads/subfolder/kernel-source-2.6.3-7mdk.rpm