Firstly clean that rust out of the drum frictional area with course emery cloth, sand paper will do if your stuck. Then before you start stripping anything down, mostly uneccersary, put a large screwdriver between the shoe and backplate one each side, difficult to explain but handles out towards you and the tip of the screwdriver at 90 degrees to the backplate. Put slight pressure on each screwdriver alternately and see if you can move the shoe, and the piston on that side of the wheel cylinder in a fraction, you only need to move it a small amount, and then the other side, repeat this about 20 times and it will show you if the wheel cylinder is seized or not. If the Pistons are moving keep moving them and they may just move in enough with the return spring pressure to cure the drag. Of course as others have said check for hand brake pivots and cable sticking by making the drum free and then putting on the hand brake and checking after release it runs free, now repeat with the foot brake. As a safety warning though if your in any way unsure please ask again or consider getting some help, steering and brakes need to be 100%, mess up the engine and the car stops, mess up the brakes.....you know the rest of this sentence ;-), help is here if you need it.
