Centralized Credential Management

Greetings!

I have a need to allow Windows 2003 to authenticate users using Active
Directory, and allow them to use a Samba file server. I would like to
use a single user store instead of a Linux store and a Windows store.
This brings up three scenarios:
1. Maintain both, but create a sync program to keep them in sync :(
2. Use AD, but have Linux use LDAP via AD for authentication. Is this
possible?
3. Use Samba as AD. This is my preferred solution, but is it
possible? samba.org web site seemed to indicate that it is, but was not
explicit. Anyone have any experience/comments on this?

Regards,

George