Does anyone know how to set up Time Machine on an external hard drive with a direct connection for the initial backup and then wireless via another Mac (i.e., as a shared drive on an old iBook) for periodic backups? I've been able to set it up both ways, but not interchangeably for periodic backups. When I do it this way, Time Machine seems to think it's a different external hard drive. I could do the initial backup wirelessly, but it takes forever. Thanks.