A couple quick commands to export/import mailboxes using the PST format in Exchange 2007.  These must be run from the Exchange Tools Console on a 32-bit machine.

Export-Mailbox –Identity <mailboxUser> -PSTFolderPath <pathToSavePST>

The following code will export all mailboxes in a selected database.

Get-Mailbox -Database 'MDB' | Export-Mailbox -PSTFolderPath D:PSTs

 The following will import a PST.

Import-Mailbox -Identity <mailboxUser> -PSTFolderPath <PSTFileLocation>

The following will import all PSTs from a selected folder.

Get-Mailbox -Database 'MDB' | Import-Mailbox -PSTFolderPath D:PSTs