Most of the credit of this post goes to http://www.geekpedia.com/tutorial207_Speaking-Computer-in-Csharp.html
How to use SAPI:
STEP 1: add reference in your project – Microsoft Speech Object Library (under the COM tab);
STEP 2: in your source code, include the namespace SpeechLib;
STEP 3: create an object from SpVoice class;
STEP 4: invoke the method Speak(string, SpeechVoiceSpeakFlags) from SpVoice.