You need to go through the computer. The only books you can get to the Nook right away are the ones you get (buy or free) from Barnes & Noble.
Install ADE on the computer (no other utility needed), authorize computer and Nook, go borrow books! (I LOOOVE "going to" my eLibrary!)
The extra step, going through ADE is really not much of a problem. It's fast and easy, especially after a couple of times when you get into it.