To avoid problems while migrating your existing server from Windows Essential Business Server 2008, it is recommended that you read this document in its entirety before you begin
More information regarding the Essential Business Server 2008 Migration Preparation Tool can be found here:
Exchange 2007 - Planning Roadmap for Upgrade and Coexistence:
Exchange Server Deployment Assistant:http://technet.microsoft.com/en-us/exdeploy2010/default.aspx#Home
Move the mailboxes.
Move the public folders (if any).
Move the user data (if any) to a new file server.