How to changing the mail server machine with 2003

I want to change a current dell server to another dell server of high speed performance.
Currently it is having MS-2000 server and MS-2000 exchange server and the new dell server will have MS-2003 server and MS-2003 exchange. Another thing I have to keep the curent user/clients updated with the mail server.
-I need a solution for the above.
- shall I use replica
-or shall upgrade to exchange 2003 and than migrate to 2003 server.