Cream margarine. gradually add sugar. Beat until light and fluffy. Add eggs, one at a time, beating well after each addition. Combine dry ingredients. Add alternately with buttermilk, beginning and ending with flour. Stir in nuts and vanilla. Pour into greased and floured 10-inch tube pan or Bundt pan. If preferred, use cooking spray to prepare pan. Bake at 350 degrees for 1 hour and 15 minutes or until cake tests done. Cool in pan 10 to 15 minutes. Remove from pan and cool completely.