Against all odds, GM and Segway let us inside their precious P.U.M.A. prototype, and we went for a quick jaunt down 18th St. We couldn't drive it, unfortunately, but there was plenty of action to be had from the passenger side. Starting from a rest on four wheels -- the main powered wheels and the front two "safety" wheels; we never touched the back two to the ground -- the contraption shoves itself up onto two wheels quite gracefully, with the passenger compartm
