I have no offical info on anything in there, but I have been able to infer a lot about the circuitry from the way it behaves (not to mention I opened one of our old ones that broke...). There's all kinds of fun stuff in there, but the guts are two PIC microcontrollers, if memory serves. I don't recall if the ADC is on the PICs or seperate... They're really surprisingly empty inside
I know somehow the "unused" I/O pins on the Stamp are connected to something that makes the LEDs and seven segment displan on the OI work. And, of course, there's no need to know any of this in order to make it work.