You can not have a NT 4.0 PDC in the same domain as a Win 2k DC.
A Win 2k can ONLY be a PDC emulator (by upgrading the PDC ) or a member
server on a NT 4.0 domain.
If you don't upgrade the PDC of your existing domain *any* Win 2k DC you
create will have a different SAM and will be in a separate domain.
There can not be a NT4.0 PDC in a W2K domain. So assuming you mean BDC, yes
W2K dc stores all user data in ntds.dit and replicates only the data with
the sam on the NT4.0 BDC that the sam has in common. A mixed mode domain
will severely limit the amount of users that the Active Directory can
contain since it does need to replicate with a downlevel BDC. --- Steve