Let me second that suggestion for caution. I've used similar software and can attest to the importance to use the right voice which also determines the price you'll pay. If you're interested in a comparison, go here
http://www.naturalreaders.com/sample.htm# and try the demos for NaturalSoft's software. Their free version comes with Microsoft's Mary voice which is awful. An AT&T voice which I found I can't listen to for more than a few minutes before giving up will require that you buy the $50 version of NaturalSoft's product. For the really good NeoSpeech voice, you have to buy the $100 version.