Active Directory (AD)

Windows 2000 and 2003 servers implement Active Directory Domain Controller

Active Directory is a combination of

DNS
Kerberos (principals for users and hosts)
LDAP (Directory entries; Group Policy for users and hosts)
RPC

No need for NTLM passwords -- they have been replaced by Kerberos

CIFS is integrated with Active Directory.

There are a few common encryption schemes between MIT Unix Kerberos and Windows AD, therefore, unified Unix-Windows authentication is possible.