Combine 2 1/2 cups water and bottled clam juice in medium saucepan. Bring to simmer. Keep warm over low heat.
Heat 3 tablespoons oil in heavy large saucepan over medium heat. Add shallots; sauti until light golden, about 4 minutes. Add rice; saute 2 minutes. Add wine; stir until liquid is absorbed, about 2 minutes. Add stewed tomatoes; cook until liquid is absorbed, about 3 minutes.
Add 1 cup clam juice mixture to rice. Simmer until liquid is absorbed, stirring often. Continue adding clam juice mixture by 1/2 cupfuls until rice is tender but still slightly firm in center and mixture is creamy, simmering until liquid is absorbed before each addition and stirring often, about 25 minutes. Heat remaining 3 tablespoons oil in heavy large skillet over medium-high heat. Add shrimp, scallops, prosciutto and garlic and sauti until shrimp and scallops are opaque in center, about 6 minutes. Mix seafood into rice. Cook 3 minutes longer. Remove risotto from heat. Season to taste with salt and pepper. Transfer to serving bowl. Stir in chopped rosemary and basil and serve. (Serves 6)