Orbital doesn't work for me as well - there was a bug relating to this in the Linux/Win32 version of the demo as well. Apparently the fix hasn't made it to OSX...
Admin stuff is easy: add the following line to the [Engine.GameInfo] section of your UT2003.ini:
AccessControlClass=XAdmin.AccessControlIni
You can then login to the web admin with Admin/Admin and change login name and password there or in the newly created XAdmin.ini file.
What I'm most pissed about though is that I can't connect to my OSX server from my WinXP client - I get "Incompatible Game File: XWeapons.u" errors.