Over medium heat in medium saucepan combine sugar and white corn syrup. Heat until it bubbles stirring constantly, 2 to 4 minutes. Mix well in peanut butter and Rice Krispies. Pat into a 9x13 buttered pan. Let cool. Melt chocolate chips and peanut butter chips or melt chocolate chips and shortening over medium-low heat in a medium saucepan and spread over cooled bars. Refrigerate for an hour if you want the chocolate to harden faster then cut into desired size squares. Serve at room temperature.