Can not add domain accounts to localgrou

We are running a Windows 2000 server that is the dc and have Win 2000 and xp clients connecting to the domian. We are able to log on to the domain and the computer accounts are in the domain and are able to do everything we need to on the domin but when we try and add a users domain account to the local computers Administrators or any group in computer management it can’t find the domain. The only location that shows up is the local computer. How come the domain does not show up?