This is a good article to read: http://blogs.msdn.com/robch/archive/2006/08/29/730032.aspx . I did a couple of searches and the only thing I found was the http://www.imptec.com/download.htm page. However they are not for Windows Vista. Search for Microsoft Anna or Sapi or microsoft tts (text to speech) if you want to search more.
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Response to CapnBuck
This is a good article to read: http://blogs.msdn.com/robch/archive/2006/08/29/730032.aspx . I did a couple of searches and the only thing I found was the http://www.imptec.com/download.htm page. However they are not for Windows Vista. Search for Microsoft Anna or Sapi or microsoft tts (text to speech) if you want to search more.