In a bowl cream together 1/4 cup of the margarine, peanut butter, and the brown sugar. Beat in 1 of the eggs and the cream cheese, a little at a time, beating until mixture is smooth.
Melt 1/2 cup margarine with the chocolate over low heat,, I did this in the microwave, on LOW heat! stirring until smooth, and let cool.
In another bowl cream together the remaining 1/2 cup margarine, sugar, beating until light and fluffy, and beat in the remaining 2 eggs, 1 at a time, beating well after each addition.
Stir in the chocolate, vanilla, flour and pour the batter into a buttered 9x13 pan.
Drop dollops of the peanut butter mixture into the batter, swirling to marble the batter. Bake the brownies in the middle of a preheated 350 degree oven for 45-50 minutes or until they pull away slightly from the sides of the pan. Let brownies cool before cutting into squares.