I haven't used redhat-network in quite a while, but more than likely you haven't registered. You have to
be a registered user w/rhn to do updates.
You don't mention which distro you are using, but if it's current FC1-FC3, then just use "yum" to do your
updates. In a root shell, type "yum update". That's all there is to it. Do a "man yum" for more options.
If you encounter timeout issues, there's a faster yum repository at freshrpms.net. See my other posts
elsewhere on LQ on how to change over to the freshrpms repository...