Another option would be to move all the other emails out of Inbox, shut down Outlook Express, and delete the Inbox.dbx file. You can find the location of the file by right-clicking on the Inbox in the folder list; choose Properties, and you'll get the full path for the file (which will probably be longer than displays in the box provided, but if you click in the middle of the name and press Ctrl+A, you can copy the entire path, and put that into the address bar of My Computer).
When OE starts up again, it'll automatically create a new Inbox.