I'm moving my Exchange Server data to a new server, but I'm not sure how to migrate the public folders. Do I need to create replicas from a particular server?

No. Exchange will replicate the information for you. All versions of Exchange maintain a separate object that describes the public folder hierarchy (i.e., which folders exist and how they're nested). Exchange replicates the hierarchy to all servers in the organization, but an individual server might or might not contain replicas of a particular folder. When you use Exchange System Manager (ESM) or Microsoft Exchange Administrator to create a folder replica, you're modifying the hierarchy object, so you can add or remove replicas from any server or workstation. As the modified hierarchy object makes the rounds, each server to which you add replicas will receive replication messages from another server containing a replica of the specified folder.