No, the audio books are just spoken books by a voice actor, with occasional background music. If they do display the text they'd have to be categorized as a movie file, as so far there is not yet a codec out there that streams audio and text together.
You could do this, by creating a movie file with only audio,and a null driver for video, while using subtitles though. To save space the subtitles would have to be an external subtitle file.
There's also another option, probably found on the jetbook color soon, is TTS (Text to Speach), where the jetbook's CPU converts text to audio. It's not as good as a pre-read book, and consumes considerably more battery, as well as there'll be no background music; but it would allow the audibly reading of a text file or book, so you won't need large files for storing video or audio data.
Unfortunately the Jetbook COlor is not as far yet to have this TTS work properly (it works by reading highlighted text though..; pretty hard to mark a whole book for reading)