I think for Fictionwise epubs you
have to install ADE. Fictionwise doesn't have the actual ebook, just an acsm pointer to the book on the Adobe server (someone correct me if I'm wrong).
I have Ubuntu Linux on my main PC (there's no ADE for Linux), so I installed ADE on an old Windows XP machine and downloaded my Fictionwise epub purchases on that PC. Then, after a
little magic courtesy of I Love Cabbages, I'm able to read the epub on my Linux machine or my BeBook.
Edit: Tech_Au beat me to it ... and explained it better.