NT Domain Authentication with Samba

I am trying to setup Samba to use Domain Authentication so I can give our domain users a home directory on the Linux storage server.

The problem is that I can’t figure out how to connect Samba to the PDC. Whenever I use smbpasswd to try to join the domain, it says “Unable to join domain”.

Does anyone have any pointers on doing this? Are there any good documents on it? The Samba docs are not very clear on this procedure.