I'm making a program, and I want the computer to be able to talk to the user, and I dont want to record my own voice becuase the quilty woun't be good

I know that its possible because programs like Bonzi Buddy (www.bonzibuddy.com) does it, they like progmraed some kind of formula into the program, so it can read what ever you type, to get a better picture of what I want download it (the monkey) at http://www.bonzibuddy.com,

I hope that it was clear

thanks in advance