At about 1005 eastern time, a flight instructor preparing a Beech BE-76 for flight suffered serious injuries after being struck by the propeller. The student pilot and one passenger were not injured and the airplane was not damaged. The student pilot stated that he was seated in the right seat and the flight instructor boarded the airplane and sat in the left seat. He said the flight instructor then said something about the starter, and before saying anything else, stepped out of the cockpit and went to the left propeller. The student said he then saw the flight instructor move the propeller, and the next thing he saw was that the flight instructor was lying on the ground.