Mix margarine and milk powder until crumbly. Add cocoa and artificial sweetener. Mix until blended. Add evaporated milk and vanilla. Mix until almost smooth and sticky. Remove from bowl and mix in Rice Krispies with hands. Continue mixing with hands until fudge is smooth and shiny. Shape into 2 10inch long rolls. Wrap in clear plastic wrap. Chill until firm. To serve, cut into 1/2 inch thick slices. Store in refrigerator. 1 serving = 1/5milk, 1/40th bread, and 1/20th fruit exchange. 30 calories.