I am about to upgrade a client's email server from Exchange 2007 to 2010. However, we will be needing to use the original server hardware (upgraded) to run Exchange 2010 so we need to either temporarily install another server running Exchange 2007 and migrate the existing mailboxes, etc. to it, then wipe the original server, upgrade the hardware, install Windows Server 2008 R2 and Exchange 2010 and migrate back, or, is there an easier way? I was thinking of exporting the mailboxes to PSTs, wiping the server and rebuilding it with Exchange 2010 then creating the new mailboxes and importing from PSTs. We have just over 200 mailboxes, total size 97 GB, average size 0.49 GB, none greater than 2 GB. This method avoids the need to migrate to a temporary server but I'm not sure what to do with the public folders that are used for shared calendars.