It can _replace_ a native W2K ADS DC as of Samba 3.0, or be its "bitch" -- i.e., a "member server" in a native W2K ADS domain. It can't, however, be a peer DC to a native W2K ADS DC, and it probably never will, at least completely.
Please explain this from the Samba Official Howto:
"Samba-3 is not, and cannot act as, an Active Directory server. It cannot truly function as an Active Directory PDC"
Are you saying that you can integrate Samba 3.0 with a Kerberos server implementation, a LDAP server implementation and dns to give a half-cooked (forget Exchange, blah) but functional ADS DC to host a ADS domain for Windows XP clients to logon to?