Sherry--
I recently worked with Symantec tech support to resolve this issue myself. I have an OS X server running 10.3.9 that is tied into our Windows 2003 Active Directory. Here are the steps that I took:
1. Install MAC remote agent on MAC server with CD.
2. Edited firewall on MAC server to allow any connection from BE server (could probably tune to specific ports, but I have not pursued it yet).
3. Added the following entries to the host file on the OS X server:
OSX_Server_IP OSX_Server_NetbiosName
OSX_Server_IP OSX_Server_FQDN
4. Added the following entries to the host file on the BE server (although I don't think this is completely necessary since the MAC server published itself successfully, but I haven't tried removing the entry):
OSX_Server_IP OSX_Server_FQDN
5. Used my domain admin backup account without DOMAIN\ or @FQDN to authenticate. When you look at the domain account that you want to use in "Workgroup Manager" on the MAC server, it has a "Short Name" list, and the first entry is the username without any sort of domain qualifier. This seems to be the only way to get a domain account to work.
After that, backup your data! I only just got this to work yesterday, and my full backup failed because the remote agent decided to crash, but I at least got to the point where I can attempt to pull the data. I also configured a separate job just for the MAC server so that I can do full backups and differential backups based on modified time and not the archive bit, since OS X doesn't support the archive bit backup method.
Hope this information helps!
Erik