Easter egg: Go to disk 1 "Play Movie". Hit right to highlight the owl to see Harry's Hogwarts letter.
Easter egg: 2nd disc: Go into the Great Hall and choose "The Quest of Sir Cadogan". During the introduction to the challenge, between the part when you see Sir Cadogan sleeping (maybe) and when he gives flowers to a girl, hit the left arrow on your remote and you'll automatically go to the picture gallery (which you will also get to if you play the challenge and get the highest rank). You'll still have to play the challenge afterwards, though, unless if you hit Menu.
Easter egg: On Disc 2, go to the Chamber Challenge in Activities and the narrator says something about a secret passage. Well, at the start instead of clicking the center forward arrow, be quick and press 'LEFT' on your remote, then it reveals the secret passage. On the U.S. release press 'LEFT' and then press 'UP' and again it shows the secret passage, bypassing the questions.