Whoa, that is a project not so easy to do for a starter...
So, what is your experience in the fields of mechanics, electronics and programming?
If you are a beginner, I sugest to get a Lego Mindstorms kit as it is verry suitable to build any kind of projects. The set has building instructions for a biped robot. You can add the moving mouth and if you study the I2C interface, you can add a voice recognition kit, a CMUcam or AVRcam, an I2C servo controller and much more. The NXT controller has an ARM7 32 bit microcontroller that supports multitasking, a graphic display (you can do the mouth in graphics if you like) and speaker, Bluetooth comunication with the PC or other NXT controllers. Lots of possibilities here.
If you take this route, let me know, I'll give you some links to check out.