I'm not familiar with OE7, but this works with OE6
Open OE. Select Tools - Options - Maintenance - Store Folder. You now know where the working DBX files are kept. In Windows Explorer navigate to that folder and simply overwrite the DBX files there with your backed up ones. A word of caution though. All your new emails will be lost, so if you want to keep them, then before doing any transferring, in OE create new folders and move all your emails into them. This will create new DBX files with different names, so they will not be overwritten.