Moving from 2000 server to 2003 server

Dear Coleagues,
I have been running AD in a windows 2000 domain, but would like to upgrade the perations Master to a Windows 2003 standard server. Actually I am not upgrading the machine itself, instead I wish to replace it with another server running Windows 2003. I do not know the best way / steps for performing this, without loosing my user accounts details and other important domain information. I also have another win2k server which acts as the backup to the one i wih to retire. Do I have to make this backup a win2003 server too. Can it remain win2000 while i introduce a new Operations Master that is running a much later OS.
Thanks