1. Place water in a large saucepan; bring water to a boil. Add shrimp and crab boil package, and cook 5 minutes. Add potatoes; return to a boil. Reduce heat, and cook 15 minutes or until potatoes are tender. Remove from heat, and let potatoes stand in water 2 minutes.
2. Drain potatoes; discard shrimp and crab boil package. Transfer potatoes to a serving bowl, and add butter and remaining ingredients. Toss well.