Advance to the last chapter and watch the rest of the movie. Press Up after the main menu re-appears until the Inspector Gadget 2 logo is highlighted. Press Play to view an alternate menu.
Hidden menu animations
Press Up at the main menu to highlight Inspector Gadget's head, then press Enter. If done correctly, Inspector Gadget's head will extend upwards and break the roof. You can also do this with other parts of his body at other menus.
Press Down at the main menu until the gear at the lower left is highlighted. Press Enter and an object will appear from Inspector Gadget's hat. Press Right to highlight another gear. Press Enter and a glove will shoot out of Inspector Gadget's hat to catch a baseball.