In a decision that will force New York City to make major changes in its system of government, the Supreme Court ruled Wednesday that its Board of Estimate is unconstitutional and violates the one-man, one-vote requirement. The Board of Estimate - composed of the mayor, the city comptroller, the City Council president and all five borough presidents - has final say on all city contracts. It was not immediately clear what impact the ruling would have on this year's city elections. The high court affirmed a 2nd U.S. Circuit Court of Appeals decision that had invalidated the board's voting system because it gives the city's five borough presidents equal power, regardless of each borough's population.