There is no writable WD SmartWare partition

I am attempting to install a new My Book Essential on my Mac, using Snow Leopard, and I am getting the message “There is no writable WD SmartWare partition” and that the WD drive may be formatted for a different OS or the drive may be locked.  I clicked on the unlock icon and got the message that it isn’t locked.  How do I check to see what iti is formatted for and how do I change it if necessary?

The My Book Essential comes out of the box formatted for Windows.  In order to use it, you will need to reformat it for your Mac.