According to the Samba documentation, Samba cannot "interact with Windows DC's in the same domain".

But, looking through my notes I have managed to join an Active Directory domain in the past, unfortunately I don't recall in what capacity the connection works. Below is a dump of my notes in hope that they can help, but I cannot provide much support on this issue.

Good luck!

joining active directory
------------------------

resources
'''''''''

resources for setting up samba+kerberos -> AD
    http://www.enterprisenetworkingplanet.com/netos/article.php/3487081
    http://www.samba.org/samba/docs/man/Samba-HOWTO-Collection/domain-member.html
    https://help.ubuntu.com/community/ActiveDirectoryHowto
    https://help.ubuntu.com/community/ActiveDirectoryWinbindHowto

dependencies
''''''''''''

apt-get install winbind
apt-get install krb5-user
apt-get install ntpdate

files to configure
''''''''''''''''''

note: uppercase matters!

/etc/hosts
    1.0.0.63     ad.example.com     ad

/etc/krb5.conf
    [libdefaults]
        default_realm = EXAMPLE.COM

    [realms]
        EXAMPLE.COM = {
        kdc = ad.example.com
        }

    [domain_realm]
        .example.com = EXAMPLE.COM

/etc/samba/smb.conf
    [global]
        workgroup = EXAMPLE                 # required when joining domain
        realm = EXAMPLE.COM
        preferred master = no
        security = ADS
        encrypt passwords = yes
        password server = ad.example.com    # shouldn't be req.
        winbind separator = +
        idmap uid = 10000-20000
        idmap gid = 10000-20000
        client use spnego = yes             # win2003 requires SMB signing

/etc/hosts
    1.0.0.1 nas.example.com nas

/etc/nsswitch.conf
    first 3 lines are most important, other vary according to the system

    passwd:     compat winbind
    group:      compat winbind
    shadow:     compat
    hosts:      files dns wins
    networks:   files dns

sync time with AD
'''''''''''''''''

kerberos is dependent on "the clock"
its recommended to sync with the active directory

    ntpdate ad.example.com

gotcha: on win2ksrv the ntp server is disabled (use regedit)

System Key: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Parameters]
Value Name: LocalNTP
Data Type: REG_DWORD (DWORD Value)
Value Data: (0 = disabled, 1 = enabled)

tips:
    - timezones are calculated, including daylight saving
    - ntp is 123/udp
    - win2ksrv will deny NTP service if its clock hasn't sync'ed with a
      NTP server in a while

        net (stop|start) w32time
        net time /setsntp:pool.ntp.org

    - ntpdate -d (debug)

restarting services
'''''''''''''''''''

i found that winbind must be started before samba
    but the docs say the opposite...

authenticate using kerberos
'''''''''''''''''''''''''''

kinit Administrator@EXAMPLE.COM

join the domain
'''''''''''''''

net ads join -U Administrator -S ad.example.com

- its recommended to change the Administrator password on win2k after
  first joining (regenerates the kerberos settings or something, not
  sure...)

testing
'''''''

# smbclient -k -L nas.example.com

# wbinfo -u

EXAMPLE+administrator
EXAMPLE+guest
EXAMPLE+tsinternetuser
EXAMPLE+iusr_ad
EXAMPLE+iwam_ad
EXAMPLE+krbtgt

# wbinfo -g
BUILTIN+administrators
BUILTIN+users
EXAMPLE+domain computers
EXAMPLE+domain controllers
EXAMPLE+schema admins
EXAMPLE+enterprise admins
EXAMPLE+cert publishers
EXAMPLE+domain admins
EXAMPLE+domain users
EXAMPLE+domain guests
EXAMPLE+group policy creator owners
EXAMPLE+dnsupdateproxy