Hi, stormingblues, Nook (unlike Kindle) supports both DRM-protected and DRM-free ebooks in ePub format thus it supports ebooks from B&N store, from any other DRM-free source on the web, and from public libraries.
First you need to get Adobe Digital Editions (ADE) software (free from Adobe site).
1. Once you have checked out a title from your local library, download it to your computer. Once you hit the download button, the file that you will be prompted to download is a “.acsm” file.
2. Click open and the file will open up in ADE and refresh your library with new content. The title will display the amount of days you have left in the loan period. You can also save the .acsm file to your PC and open the file in ADE.
3. Go to the library view. Drag the title to the “NOOK” icon.
4. Undock the NOOK from your computer.
5. In the Library, open My Documents.
6. The title should be available to be read for the period of time specified by the library.
Also, here's the longer step-by-step I found on in the forums:
Setup ADE on your computer
Open ADE and the “Setup Assistant” will be displayed
Click “Continue”
The “Authorize Computer” box will display
Enter your Adobe account information
Click “Activate”
Click “Finish”
Authorize ADE on your Nook
Connect the Nook to your computer via the USB cable
Open ADE
ADE should “see” the Nook and the “Device Setup Assistant” box should appear.
Click “Authorize Device”
If ADE does not “see” the Nook, try the following steps.
Go to “My Computer” (or the equivalent on your PC or Mac) and click on the Nook drive.
Find and delete the “.adobe-digital-editions file.
Close ADE
Restart ADE
Your Nook should now be visible to ADE, if not
Go back to the Nook drive
Find the “Digital Editions” file and delete it
Close ADE
Restart ADE
Nook will be visible
Click “Authorize Device”
Downloading eBooks
This is not a standard download like you have seen or used in the past, this download is an .acsm link.After you purchase or borrow your book, click the download link or box
You should be asked if you want to open (do NOT choose to “save” the book) in “digital editions” click yes, if you are given the option to ALWAYS open the .acsm link in this program, choose yes or put the checkmark in the box.
ADE will open and your book will be downloaded into ADE
If you do not have the option to always use ADE to download the following steps will allow you to opt in for this
For Windows:
Go to Start-->Control Panel-->Default Programs-->Associate a file type or protocol with a program
The “Associate a file type or protocol” window will pop up.
Under the “Extensions” heading, select '.acsm' and click the “Change program…” button.
The “Open With” dialog box is displayed.
Click the “Browse…” button.
A second “'Open With” dialog box is displayed.
Browse to 'C:\Program Files\Adobe\Adobe Digital Editions and select 'digitaleditions.exe'.
Click “Open”. Adobe Digital Editions is now set to open ACSM files automatically
For a Mac
Control-click the 'urllink.acsm' file and select 'Get Info'.
The 'urllink.acsm Info' window is displayed.
Expand the 'Open with:' section and click 'Other…'.
A list of programs is displayed.
Select 'Adobe Digital Editions'.
Check the 'Always Open With' checkbox.
Click the 'Add' button.
Close the 'urllink.acsm Info' window.
Adobe Digital Editions is now set to open ACSM files.
How Do I Get the Book on my Nook?
Once everything is downloaded, installed and authorized, this is the easy part! Just "grab" the book (that you have previously purchased or borrowed and downloaded into ADE) you want to copy to your Nook, drag it over to the "Nook" (on the left hand side of ADE) and drop it in!