Preheat the oven to 375 degrees F (190 degrees C).
In a large bowl, cream together the peanut butter, margarine, brown sugar and white sugar. Beat in the eggs and vanilla. Combine the flour, baking powder and baking soda; stir into the peanut butter mixture. Form dough into walnut sized balls and place them 2 inches apart onto ungreased cookie sheets. Dip a fork into flour and criss cross each cookie to flatten slightly.
Bake for 12 to 15 minutes in the preheated oven, until just lightly browned. Allow cookies to cool on baking sheet for 5 minutes before removing to a wire rack to cool completely.