Hi,
You may use MS Speech SDK 4.0/5.0 or MS Agent for your purposes. The differences of both are:
MS Speech SDK - allow more control to Speech / recognition engine, more voice sample, more function....and so on
MS Agent - fewer control, only allow simple function like listen(let user speak in) , speak for TTS engine...and most special things is animation of Characters of speech.

I am developing ReadAssistant currently with using MS Agent and tried MS Speech SDK too previously. It can be added in VFP 5/6.0 as OLE object...

Let's download it from MS. It free.

Hope it helps