There are some built-in sound in TTS(Text-to-speech) like sam at XP and ana for vista, is there any way to add own sound in it.
I did a bit of research, and this site offers a toolkit to build your own TTS voice based on the (sapi-compatible) Festival TTS engine. I can't make any comments on the voice quality. The Microsoft TTS engines don't support user-generated voice construction.
There are other vendors out there (I seem to recall that AT&T Natural Voices supported user-generated voices), but most of them are extremely expensive (several tens of thousands of dollars).