United States troops have begun moving through downtown Baghdad.United States Officials said members of the 3rd Infantry Division began driving through the center of the Iraqi capital on Saturday.They said the unit did not sustain casulties.'This was an operation conducted by two task forces of the Third Infantry Division,' Major General Eugene Renuart Chief of Operations for Central Command, said.They had been south of the city and conducted a raid through the city, proceeding North to the Tigris River and continuing out to the West in the direction of the airpoirt.'Officials said the show of United States troops was meant...