Assuming pure water:
Best case likely scenario, it blew out the freeze plugs and screwed the radiator.
Worst case scenario, head or block crack (and worse) necessitating engine replacement.
Suggested course of action:Take a propane heater outside to the car and warm the block and radiator to at least 70F. Watch for leaks. Do not try to start it until the block is thoroughly warmed by the heater. Once the block has heated, drain the now liquid water out of the engine and refill with antifreeze. Watch for more leaks. While you're waiting, pull the spark plugs and determine if there is any water in the cylinders - be careful that no crap falls into the cylinders. If water is not present, spray a generous amount of penetrant into each cylinder. Wait at least 5 minutes for the penetrant to work its way in. Attempt to start the engine with the plugs out once the water has thawed and you've replaced it with coolant. If the engine spins properly, try it for a couple of seconds to get the last of the penetrant out, then refit spark plugs and try to start it 'for real.'
Chances are pretty good the thing's hosed, though.