Preheat oven to 400°. In a large saucepan, bring water, butter and salt to a boil. Add flour all at once and stir until a smooth ball forms. Remove from heat; let stand 5 minutes. Add eggs, 1 at a time, beating well after each addition. Continue beating until mixture is smooth and shiny.
Using a tablespoon or a pastry tube with a #10 or large round tip, form dough into nine 4x1-1/2-in. strips on a greased baking sheet. Bake 35-40 minutes or until puffed and golden. Remove to a wire rack. Immediately split eclairs open; remove tops and set aside. Discard soft dough from inside. Cool eclairs.
In a large bowl, beat milk and pudding mix according to package directions. In another bowl, whip cream until soft peaks form. Beat in sugar and vanilla; fold into pudding. Fill eclairs (chill any remaining filling for another use).
For frosting, in a microwave, melt chocolate and butter; stir until smooth. Stir in sugar and enough hot water to achieve a smooth consistency. Cool slightly. Frost eclairs. Store in refrigerator.