In this post the MSExchangeTeam explained to use how to import and export PST files in Exchange Server 2007 SP1.
There might be times when an Exchange Administrator will need to export the contents of individual mailboxes to offline files in order to present specific users with a format that is easily portable and ready to consume using Outlook clients. To fulfill this need Exchange 2007 SP1 will have a new set of features to export and import mailboxes to and from PST files. As I know you will ask - yes, those PST files can be bigger than 2 GB, which was a limitation of Exmerge tool used for this purpose in previous versions of Exchange.
Read more at: http://msexchangeteam.com/archive/2007/04/13/437745.aspx