As the above diagram shows, the V2 contains quite a few circuit boards. The Foot and Hand board are simply used to connect to the sensors and motors (and batteries in the case of the Foot boards) in the respective limbs and contain no real circuitry. The power board is also fairly simple, just a connection point for the power switch and speaker. The Head Board is more complex, but only because it contains more connectors.
The Camera board is dual purpose, it contains all the circuitry for the camera as well as IR diodes used for object detection and interaction with other wowwee robots. The Motor board is the most packed circuit board, containing at least 88 transistors and numerous diodes and resistors, its function is fairly simple though, to provide simple motor control to the Main board.
Finally we come the to the Main board, this board is the brains of the V2. It is the most important board in the V2, since it connects to almost everything directly, and everything else indirectly. It also converts the battery power to different levels for use with the sensors and camera.