Install Adobe Digital Editions (ADE) on your computer (it's free).
From your library web site, when you select the ePub format and tell it you want to borrow the book, it will automatically download the book to your computer, and the book will show up in the ADE.
Connect your NOOK to your computer with its USB cable. The NOOK will appear as a new device in ADE.
In ADE, drag the book from "All Items" to the NOOK entry. That will copy the book to your NOOK.
Before disconnecting the NOOK from the computer, "eject" it in Windows Explorer. If you don't, you will sooner or later have phantom books on your NOOK.
Apps don't work in the NST. According to the 3M site, you can download the 3M PC one Mac app and use it to copy to your NST. http://3m-ssd.implex.net/cloudapps/ Fulltimervr I don't believe 3M uses ADE. Based on the 3M site you have to download their PC app to transfer the books.
Thanks bklvr896! I still haven't been able to download my library books to the STG, but you pointed me to the website and further investigation. There is actually a video of how to download books to the ST!
They do mention that it isn't able to sync with other nooks though.
I haven't been able to do it yet as it asks for login and password information which doesn't correspond to anything I tried. I called the library and stumped their expert - the one responsible for installing the program. (It's quite new at our library, and offers a very limited supply of books at this time. He will get back to me when he figures it out!
So there is a way.....