Combine sugar and corn syrup in a 2-quart microwave-safe dish, and micro-cook on High 4 minutes. Stir in roasted peanuts, and micro-cook on High three to five minutes, or until lightly brown. Add butter and vanilla to syrup blending well; micro-cook on High one or two minutes more. Add soda to mixture and gently stir until foamy. Pour onto a greased cookie sheet. Let cool; break into pieces when fully cooled.