If you're running Calibre on Windows you could try MobiCreator to do the conversion
My experience is that Mobicreator often produces 'better results' than Calibre - without experimenting with lots of settings. It creates PRC files, not sure if Stanza can read PRC, but Calibre does a good job on converting PRC to ePUB or one of the other formats that Stanza supports.
I also just stumbled on another converter from Hampster Soft (thanks to member Dullahir). It seems to produce better results than both MobiCreator and Calibre, its simpler to use than Mobicreator, and it can create an EPUB directly.
If you install it the Hampster Soft program watch out for the Open Candy stuff, and make sure you do a custom install - otherwise you'll end up with AVG toolbars in your browsers etc etc <grhhh>
Last edited by BetterRed; 04-29-2013 at 10:07 PM.