Forgot ID for WD My Book Essential

Hello,
My husband set up the WD external Harddrive and backed up all our irreplaceable information on our Mac Mini. We knew the hard drive was going bad and we were able to get everything was backed up. We replaced the internal HD in the Mac Mini and quadrupled our memory. Now we are trying to retrieve all our pictures and other backed up data. My husband was able to unlock the drive but when we try to install the HD in our "new" Mac Mini it is asking us to authenicate with the User ID and password. My husband can not remember the ID used when it was all set up so we can not get into the external HD. He's "positive" he remembers the password if we can just figure out the ID.

Is there anyway to retrieve our information? Either the ID used or our saved files? When installing the HD on the new Mini HD do we have to partition it again? Someone Please help!! We tried calling WD and no one could help us. The said to call back tomorrow when the "Experts" are in?!?!?!?!?!?!?!