Hi,
I like to do things like this:
1. Install support tools from the server cd on both servers.
2. Run DCdiag on the DC server to check all is well. Run Netdiag on DC
also.
3. Run Netdiag on new server, patch it, etc.
4. Promo DC2.
5. Wait a bit for replication. Run DCdiag on both DCs to make sure all is
well.
6. Grab FSMO roles and transfer to DC2.
HOW TO: View and Transfer FSMO Roles in the Graphical User Interface
http://support.microsoft.com/default.aspx?scid=kb;en-us;255690
7. DCDiag both servers.
8. Make sure WINS, DNS, DHCP, etc are transfered. Transfer any file shares.
How to move a DHCP database to another Windows server
http://support.microsoft.com/default.aspx?scid=kb;en-us;130642
How to move Windows 2000 DNS zones to another Windows 2000-based server
http://support.microsoft.com/default.aspx?scid=kb;en-us;280061
(I usually make DC's DNS AD integrated for this step)
9. Turn off DC1 for a bit to test DC2 is coping ok. Then promo DC1 down.
Remember you can't rename DC2 afterwards so choose your names carefully.
