And if the brakes won't stop the car, try the key switch! An engine that is not running will not cause acceleration. (Sure there are probably some oddball push-button ignitions that can't be turned off while in gear, but most vehicles can be.)
* This was what made the GM Ingnition switch problem so deadly. The engine shut off (taking power steering and vaccuum-assist braking with it) and the airbags deactivated making any subsequent crash less survivable.