I registerd it via Wifi. I only typed in my B&N account information (email adress and password). But it has to be the same mail and password, as you have the account at B&N.
After that, it connected automaticly to my B&N account and I could surf thru the shop, download samples and download contend that I had already bought online in my account. You cannot buy books direktly from the nook.
If you have more questions, guess it is easier to handle them in the German forum here. At least it is easier for me to explain
