ExMerge Exchange 2003:

Mailbox Merge Wizard (ExMerge) : Use the Mailbox Merge Program to extract data from mailboxes on a Microsoft Exchange Server and then merge this data into mailboxes on another Microsoft Exchange Server. The program copies data from the source server into Personal Folders (.PST files) and then merges the data, in the Personal Folders, into mailboxes on the destination server. The ability to merge data to and from an Exchange Server makes this program an invaluable tool with a variety of uses- especially during disaster recovery. The program can also replace existing data instead of merging new data if specified by the Administrator. Mailbox Merge has some limitations. Please read the tools documentation before using this program. This utility comes with the exchange CD otherwise you can also download using the link given below:

Download
http://www.microsoft.com/downloads/details.aspx?FamilyId=429163EC-DCDF-47DC-96DA-1C12D67327D5&displaylang=en