It seems that this is a Samba issue and not a FDS issue. I hadn't locked on to the fact that Samba is the Domain controller and FDS is only the Directory server.
I can't figure out how to add a computer to the domain.
I've searched but can't find anything on this, which I assume means it is so easy that no one has even bothered to write about it.
I created a user in the Domain Admins group. I made that user an NT User, set the NT User ID to be the same as the FDS User ID, and checked Create New NT Account.
On a Windows XP box I went to System Properties->Computer Name->Computer Name Changes and entered the domain name.
I am prompted to enter the name and password of an account with permission to join the domain. I have tried entering the user name both as domainname\username and just username. No matter what I entered I get:
"unknown user name or bad password"
I also tried adding a similar user (different User ID) to the Directory Administrators group. Using that user produced the same result.
If someone could please explain what needs to be done, or point me to a doc no this very basic process, I would appreciate it.