Unfortunately, it sounds as though the engine overheated, probably warped the head and water mixed into the cylinders. Check for signs of water in the oil or oil in the cooling system. The following link describes the usual suspects for engine smoke:
Car Engine Smoking | Car Trouble
Don't start the car! If the fluids have mixed, you could seize the engine by running it. I'd recommend performing a compression test and if possible a leak down test to help diagnose the problem.