If you've accidentally deleted a file in Outlook 2007, and then emptied the Deleted Items folder, there is a chance that it's still recoverable.
Select the Deleted Items folder, click on Tools and then Recover Deleted Items. You should be presented with a list of e-mails and folders that have recently been removed from the deleted items list.
Select the e-mail you want and click the recover button. Or select everything and purge it with the big X button.