In Slick Willy's River Boat (level 3), you have to ring a bell. Go to the front of the boat where about two or three steps are located. Go up to the steps, then go back slightly. Press R3 and Frogger will look up. Shoot the bell three times pressing Square. All doors will become unlocked. Go to the very top of the boat and go over to Slick Willy (the alligator). Fight him and win. Defeating him is not difficult - just go over and keep hitting or kicking him. You can now take his speed boat and go to the next level.