I think you might have to turn the file in to text, before you can have software speech turn it in to audio to send to the bookport. If you want to use bookport and doubletalk, none of this work is necessary. nfbtrans will back translate the file in to text, and their is a windows interface for the dos nfbtrans program to allow you to do the job from within windows. Sounds like a lot of work to me, but I like doubletalk just fine. I don't have the links for the translator or the latest version of nfbtrans, but Google does.
