In large bowl, blend sugar, margarine and chocolate; add eggs, one at a time, until well blended. Mix in vanilla. Combine flour, baking powder and salt; add gradually to chocolate mixture, mixing well after each addition. Cover and chill 2 hours or overnight. Drop mixture by rounded teaspoonful into powdered sugar, coating lightly, then shape into balls. Place on greased baking sheets, 2 inches apart; flatten slightly. Bake at 350 degrees for 12 to 14 minutes or until done. Remove from baking sheets onto wire racks to cool.