try howstuffworks.com
accelerator pedal pulls a throttle cable from ur engine bay which
controls a few things.. i believe ur valves and the fuel
regulator..
there are 2 types.. the older ones use throttle cable.. new cars
come with e-throttle..
speed limiting device is in ur ECU.. once u reach the certain speed
limit, ur ECU will cut the power of the car..
these are just basic information.. for more, go to the above site
or wikipedia.