1. In a microwave-safe bowl, combine the peanut butter, brown sugar, corn syrup, margarine, and vanilla. Heat on high in microwave just until ingredients melt (1 to 2 minutes). Don't let the mixture boil.
2. In another bowl, combine corn flake cereal, crisped rice cereal, and salt.
3. Pour the peanut butter mixture over the cereal and mix well. Pour the mixture into a greased 8" x 8" pan and pack it down.
4. Refrigerator for 6 to 8 hours (if you can!).
Variation: Add in 1/2 cup coconut flakes and 3/4 cup raisins with the cereal.