Parboil the potatoes: Add halved potatoes to a large stock pot, fill with water to cover. Boil potatoes until just fork tender. Drain.
As the potatoes are parboiling, fill the largest stock pot you can find (it needs to be BIG!), 1/2 way with water. Add Old Bay, garlic, beer, onions, and salt. Bring water to a boil.
Add parboiled potatoes, corn, sausage, and lemons. Simmer for 10 minutes.
While simmering, slice the fresh bread in to 1 inch thick slices, and broil lightly.
Add clams and shrimp to the pot last, simmering for about 3 minutes, or until shrimp JUST turn pink. DO NOT OVERCOOK! Shrimp have a tendency to get rubbery when overcooked. Not good!
Drain the liquid (you'll need a buddy!), but reserve about 3 cups of the cooking liquid for serving. Spread the shrimp boil over a newspaper lined picnic table (this is any outdoor meal, folks).
Enjoy immediately with remaining 2 lemons cut in to wedges, Old Bay, cocktail sauce, melted butter, french bread, and plenty of cold beer.