SAPI 5.1 versus 5.3

How to check which version of SAPI you have:
Go to C:\Program Files\Common Files\Microsoft Shared\Speech and right click on sapi.dll and select Properties. Click on the Version tab to see if you have version 5.1.

SAPI 5.1 overview
http://www.answers.com/topic/speech-application-programming-interface
Provides a nice overview of the different versions of SAPI.
http://www.microsoft.com/speech/techinfo/apioverview/
Brief overview of SAPI 5.1 and SAPI SDK 5.1 from Microsoft.

SAPI SDK 5.1
http://www.microsoft.com/speech/download/old/sapi5.asp
Download the "previous" version (before the current SAPI 5.3) of the SDK here.

Sapi 5.1: clarifications there of
http://blindprogramming.com/pipermail/programming_blindprogramming.com/2006-February/004794.html
E-mail thread that discusses how to use SAPI 5.1. Key take aways:

• Can't use SAPI 5.3 on Windows XP.
• You can use SAPI 5.1 with managed code in VS 2005 by adding it as a COM reference, and VS 2005 will automatically create the COM interop code.
  

The Windows Vista Developer Story: Speech
http://msdn2.microsoft.com/en-us/library/aa480207.aspx
Describes the features of SAPI 5.3.

All the Cool Developers use Speech APIs
http://blogs.msdn.com/chuckop/archive/2006/11/24/microsoft-speech-api-sdk.aspx
Describes the difference between SAPI 5.1 and 5.3.