tomtom tts is very cool. check out the demo here on a go:
http://www.youtube.com/watch?v=fBLBycqf574 however, i dont think it will work. other than the speech files and the voices, you also need the tts engine. tomtom uses loquendo tts engine in their go, which run under linux, and unless tomtom port it for windows mobile, it probably wont work under the touch. i'm aware that igo8 also ues the loquendo tts engine, but doubt it will work with tomtom navigator.