DHCP move question

I currently have an NT 4 domain containing 1 PDC which is only running DHCP,
2 BDC's and 1 Windows Server 2003 machine.

I want to move the DHCP database from the NT 4 PDC onto the W2K3 machine and
ensure that all client PCs can still access the network before I finalise the
upgrade to a W2K3 AD domain.

I know how to move the database but how do I get the client PCs to look at
that machine instead of the PDC?? Can this be done? IS it a manual change on
each client PC?

Will I have to undertake this when all users are off the system?

Help!!

Gary