Actually, FSPilot747, as a CFI myself, I can tell you that you only need a third class medical to be a flight instructor. You can get all your ratings with a third class medical, but to exercise the priveleges (sp?) of a commercial license, you must hold at least a current second class medical, and as an ATP, a first. You are correct in saying that in order to be a flight instructor you must first attain your commercial license, but only when using that license in anything but flight instructing do you need more than a third. Actually, a flight instructor need not even hold a medical certificate if he/she is giving instruction to someone who is rated and current in the airplane that is being flown. There is also no difference to that fact for CFII or MEI
pilots. They all require a minimum of a third class medical.
There are 3 types of people in this world, those that can count, and those that can't.