How to export a mailbox from Exchange 2007 SP1 to a PST file:
Prerequisites: You will need a machine with a 32-bit version of Windows (Windows 7 is fine) and Outlook 2003 or 2007. Join the machine to the domain that contains the Exchange server. Log on as a domain administrator. Install Exchange Server Management Tools 2007 SP1. To achieve this, insert the Exchange disc, do a custom installation, and only select the Management Tools.
Open Exchange Management Shell.
Give the current user permissions to the mailbox you want to export: