Links I Like: csounds.com, Csound Magazine, Buzz Tracker, Harmony Central, musicdsp.org

Books I Like: Computer Music (a must), Computer Music Tutorial, The Csound Book

It wasn't additive synthesis. The technique you are referring to (i think) is Linear Prediction Coding (LPC). It's the same thing that was used in technologies like the Speak'n'Spell and Dr. SBaitso. You may also remember the voice of Joshua in Wargames.