I assume you have a W2K domain with 1 Exchange 2000. You want to move mailboxes et PF (Public Folders) on a 2nd Exchange 2000 (new server).
Install your 2nd Exchange server in the same organization. Once installation's done, go in ADUC (Active Directory Users and Computers), right-click a user you want its mailbox to be moved, select "Exchange Tasks". A wizard opens. Select the "Move mailbox" task and provide informations to the wizard (that is: the destination server). Go to the end of the wizard: your mailbox has been moved.
For public folders, go in the Exchange System Manager, expand the tree down to "Public Folders instances". Select one PF, and then open its properties. You can configure a second server to host the replication of your PF. Once configured, wait for replication (replication time depends on amount of data of course).
Once your mailboxes are moved and your PFs are replicated, you can uninstall the first Exchange 2000 (before doing it, check Technet to be sure everything is OK before "deleting" the 1st server).
Hope this will help.