I also had trouble trying to do this all on the PE. If you can, first get the book into Adobe Digital Editions on a PC or Mac, and then drag it from the Adobe program onto a miniSDcard or thumbdrive or via usb to your PE.
Take a look at this tutorial for the nook:
http://beingruth.com/350/tutorial-li...ook-overdrive/
When I connect the PE to my computer, it shows up as 'Edge' on the left column of Adobe Digital Editions, and the books can be dragged onto it from the main 'Library' window.