Combine the first 5 ingredients in a large bowl; stir well, and set aside.
Place potato in a saucepan; add water to cover, and bring to a boil. Cover, reduce heat, and simmer 5 minutes. Add peas; cover and cook 7 minutes or until peas are crisp-tender. Drain and rinse under cold water; drain well.
Add vegetables to sour cream mixture, and toss gently to coat. Cover and chill. Stir before serving.