You want your Samba clients to authenticate against Active Directory and access Active Directory resources.
Samba 2.2 currently does not provide Active Directory support. The next release, Samba 3.0, which is in Beta at the time of this writing, will provide client-side support of Active Directory. OpenLDAP and MIT Kerberos must also be installed on the client to provide full LDAP and Kerberos functionality.
Samba has a rich history of providing Unix integration and interoperability solutions for the Windows network operating system (NOS) under Windows NT. Samba is typically deployed so that Windows-based clients can use Unix-based file and print services seamlessly. A Samba server can also act as a PDC in a Windows NT 4.0 environment. Do not expect this level of server emulation for Active Directory domain controllers any time soon.
For more information on the Samba project, see http://www.samba.org/.