Outllook 2003, Outbox emails not leaving.

In Outlook 2003, the Outbox is retaining email (usually those with pictures attached).  I cannot delete them because it says they are in the process of being sent.  Nor will it let me move them to another folder, like deleted folder.  But after days it has files have not left the Outbox.  Any ideas how to delete these.  They are now to old to be useful and seem to be sitting in front of newer messages that eventually go but seem to take a long time to leave the outbox.