I am developing a Interactive Spoken Dialogue System, in which user will say something to the system and system will answer him in voice and generating facial expressions according to the voice.
But, i can't get any idea that how can i generate facial expressions.
Will anybody tell me that how can i start or if there is any open source package already exists then it would be very nice.
If anybody know about any open source software related to this then please tell me.

You need to know how to use time. Every GUI got time that run. You need to bind the movement and speach with the time. Very simple. You must also know the length of the audio you want to use. You show give the same time for both animation and sound......

Hope this help.