Harold Noskin is the long deceased caretaker of the Witch's Coven Library.  Click his picture to see a video of Harold talking.  He is a very simple audio-animatronic made using Scary Terry parts.  Check out Terry's website to see how to make a talking Bucky Skull.  I used his how-to verbatim, so I don't have anything to add in regards to the mechanics.

I will put in my two cents about audio.
As I mentioned, I used Scary Terry's audio board to drive the servo controlling Harold's mouth.  I did find a bit of a lag between the sound and when the mouth moved.  This has nothing to do with the board, but rather the physics at work.  With the circuit board, the sound from the line in drives the mechanical motion of the servo.  Because the servo takes time to move, the motion will be slightly behind the audio.  When humans speak, the motion of our mouths and throats drive the sound that is produced.  Our mouths and throats begin moving before our voices are audible.  In effect, for accurate animatronic movement, the motion needs to start miliseconds before the sound can be heard.  I achieved this effect by shifting the left audio track of Harold's voice slightly ahead of the right.  I plugged the left into the servo driver and the right into the speaker.  The sound that was actually driving the servo is never heard.
Here, you can see that the left audio track is identical to the right, but slightly advanced.  If you click the picture, you can hear the two tracks overlapped.
The isolated left audio track is the 'unheard' raw audio recording of the voice.  One of the other issues with driving the servo with the finished audio track are the added treatments to the sound - e.g. adding reverb, echo, noises that you don't want driven by the servo.  Things like reverb can effect the quality and character of how your servo moves.  If you isolate a clean audio track, the servo movements will also be clean and crisp.
The selected track here is the one I want my audience to hear.  It is the delayed track with added reverb and tweaking of the sound for effect.  Click the picture to hear Harold's "voice."
Driving servos with a separate audio track is a very good way to keep your animatronics looking and sounding great.  I used no other audio source but the voice, however, I could easily add underlying music or effect to the right channel track.  It would then be heard from the speaker, but would not mess with my servo driver, mothing the servo to the music rather than the dialogue.  Additionally, you can independently control the volume of the left and right in order to have enough power to drive the servo while still maintaining a lower volume for the speaking voice.

Visit my
Jack O'Lantern how to page for more audio information.