Try to download one of this plug-in :
- Speaksforitself plug-in
- Talker plug-in
- Speech plug-in
and visit the famous :
- http://speech.apple.com/
- http://product.info.apple.com/productinfo/factsheets/speechapi.html
If you think is useless, you can see :
- news://comp.speech
look an old link ?