Preheat oven to 350 degrees F.
Microwave chocolate and margarine in a large microwaveable bowl on high for 2 minutes or until margarine is melted. Stir until chocolate if completely melted.
Stir sugar into melted chocolate. Stir in eggs and vanilla until completely mixed. Mix in flour until well blended. Stir in nuts. Spread in greased 8 inch square pan.
In the same bowl, mix cream cheese, sugar, egg and flour until smooth. Spoon over brownie mixture; swirl with knife to marbelize.
Bake at 350 degrees F. for 35 minutes or until a wooden toothpick inserted in center come out almost clean (do not overbake). Cool in pan and cut into squares.