The certificated pilot (receiving tailwheel instruction) executed a landing to runway 03, and after the airplane touched down, it drifted left. The flight instructor joined him on the controls, and added power and right rudder; however, the left main landing gear struck a 2 1/2-foot snow bank. The airplane swung to the left, the right main landing gear then struck a snow bank, and the airplane nosed over. Winds were 10 degrees from the right, at 6 knots.