Hello,
Underneath the speed/pitch/volume sliders there is a drop down menu which should contain a list of the voices available.
It is easy to miss this menu as it appears blank when the program first loads.
To be honest, I do not think you will be happy with many of the free voices given. I personally would go ahead and purchase some new voices from somewhere like Cepstral or Neo-speech. I use Cepsral Amy. Cepstral comes with its own text to speech reader too.
Hope this helps.
Echo.