Ok, I understand why you want to do this now. Will you be removing the old Exch2000 server from AD?
You use the 3 step process:
1. Move public folders & system folders(offline address book, Schedule.. etc..) to your new server in the same routing group
2. Move the mailboxes to same new server
3. Delete the old server from AD
How to
1:
Exch sys manager to replicate folders to new server. confirm replica folders are synchronised with the source (from old server)
2:
Use Exch sys manager or exch task wizard in Active Directory Users & Computers to move all mailboxes to new server.
3:
Run the Exch setup program to uninstall the server and remove it from AD, you may want to keep the Exch200 install but just remove it from AD for a rainny day.