Some can't be downloaded AFAIK. If you look at the books page in their ebook store (as opposed to the Google books page linked above) it will tell you some things about what's available. In this case both Flowing text and Scanned pages are available and it says it's Nook/Sony compatible which would mean some kind of ADE based download (ePub or PDF) AFAIK.
eBook Store page...
http://books.google.com/ebooks?id=sw...store_bookcard