1. Peel potatoes, and cut into cubes. Place potato in saucepan; add water to cover. Bring to a boil; cover, reduce heat, and simmer 15 minutes or until tender. Drain and let cool.
2. Place green beans and corn in a saucepan; add water to cover. Bring to a boil; cover, reduce heat, and simmer 5 minutes or until beans are crisp-tender. Drain and let cool.
3. Combine potato, green beans and corn, red bell pepper, and green onions in a bowl. Combine sour cream and remaining 5 ingredients; stir well. Pour sour cream mixture over potato mixture, and toss well. Cover and chill 2 hours.