danny sanders

It would be easiest to first replace the NT 4.0 DCs then once that is done
upgrade to Win 2k.

Install DNS on C and make it a secondary zone of A and allow it to
replicate.
Use Scopy from the NT resource kit to copy files from A to C and retain
their permissions.
Promote C to PDC, remove A from the network, rename C and change the IP
address to match A and reboot.

Repeat for C and D.
I would suggest having D end up as a Win 2k DC also. Then you can set your
AD DNS zone as AD integrated.

hth
DDS W 2k MVP MCSE