Valkyrie--
The link that Madam Broshkina's should answer your question very well. I've found that some libraries carry only Audio books for download, some have audio books and Adobe DE and some also have mobipocket (which won't work on the Sony.)
I personally have cards from the Sacramento Library, the San Jose Library, and the Santa Clara library. I use all three for downloading. Of these three, San Jose has the most Adobe DE formatted books (2978), while Santa Clara has 1566 and Sacramento has 690.
dordale