Soak rice noodles in cold water 30 to 50 minutes, or until soft. Drain, and set aside.
Heat butter in a wok or large heavy skillet. Saute chicken until browned. Remove, and set aside. Heat oil in wok over medium-high heat. Crack eggs into hot oil, and cook until firm. Stir in chicken, and cook for 5 minutes. Add softened noodles, and vinegar, fish sauce, sugar and red pepper. Adjust seasonings to taste. Mix while cooking, until noodles are tender. Add bean sprouts, and mix for 3 minutes.