Workgroup domains can be changed in /Applications/Utilities/Directory Access.app, Macs can be added to Active Directory there as well. Though the process in Tiger is much better integrated than that of Panther.
At my work, I just log onto the domain with DOMAIN\username and my password. Doesn't seem as easy on OS X, but I'll figure it out. Hopefully the IT guy (heh it's an IT company) knows some of this terminology.