Hi Nita,
Text to Speech only works on text and html files (not epub or pdf) if you look at http://shkspr.mobi/blog/index.php/2009/12/review-elonex-511eb-from-waterstones/ and search "Text to speech" (without quotes) you'll see a comment made by both Terrence and Scooba?!?! 🙂
Cheers
Darren