The Boston Public Library (BPL) recently announced their Digital Audio Books program. Library patrons can now download audio books to PCs or iPods some digital media players. The new site looks much like Amazon.com, and boasts downloads at anytime.
Access to the site is limited to library patrons with a library card only. If you do not already have a physical library card, learn more about instantly obtaining a BPL eCard.
Keith Munsell 
Where does it say support for iPod?
There’s a link on the left of that site which says “iPod/Mac users click here” and links to this text:
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Why can’t I transfer OverDrive Audio Book titles directly to my iPod, or use these files on my Mac?
OverDrive Audio Book titles, provided by OverDrive, Inc., use DRM protection technology from Microsoft Corporation. Unfortunately the iPod and Mac do not currently support DRM-protected Windows Media Audio (WMA) files.
OverDrive, along with hundreds of online digital media providers, is hopeful that Apple and Microsoft can reach an agreement that would enable support for Microsoft-based DRM-protected materials on the iPod and Mac.
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So iPod users are out. Drilling through the FAQ I eventually found a link to a list of supported devices.