You haven’t actually asked a question here. Are you trying to do this and have had problems? Are you looking for information before you being?
In our organization once we had the Exchange 2007 server built and a Public Folder mail store mounted we just replicated the folders to the ex2007 public folder store. Once they were replicated over we took the old 2003 public folder store off line.
You can do this as a bulk operation using PFDAVAdmin Public Folder tool. Install it on your pc, not the exchange server. You can also check replication status using this tool. It is also valuable for many other public folder operations for both Exchange 2007 and Exchange 2003.