Peel and devein shrimp. Bring water to a boil; add shrimp, and cook 3 to 5 minutes or until shrimp turns pink. Drain well; rinse with cold water. Cut each shrimp in half crosswise, and place in a small bowl.
Combine sour cream and next 5 ingredients, stirring well. Add sour cream mixture to shrimp, and toss gently. Cover and chill thoroughly.
Cut cantaloupe in half crosswise with a sharp knife to form 2 large cups; remove and discard seeds. If needed, slice about 1/8 inch from bottom of each melon half so that it will sit flat. Spoon shrimp mixture evenly into lettuce-lined cantaloupe halves.