NEW YORK - The city's yellow taxi fleet will go entirely hybrid within five years, Mayor Michael Bloomberg announced Tuesday...In addition to making the yellow cab brigade entirely green within five years, the city will require all new vehicles entering the fleet after October 2008 to achieve a minimum of 25 miles per gallon. A year later, all new vehicles must get 30 miles per gallon and be hybrid. Bloomberg made the announcement on NBC's "Today" show.