Mix Melted Margarine, Cracker Crumbs, Powdered Sugar And Peanut Butter. Spread In A 9" X 13" Pan, Pressing The Mixture Even. Melt The Chips And Pour Over The Top Of The Pan. Chill 30 Minutes, Cut Into Bars, Then Return To The Refrigerator. Note: Be Sure To Cut Within The First 30 Minutes Or The Chocolate Will Be Too Hard To Cut Well.