When the episode begins press the "audio" button on your DVD clicker and select option 5 which is also an "english" option for a hidden commentary.
-Lisa the Simpson
When the episode is playing and professor provalones brain teaser first appears pres "6" on your DVD clicker to take you to a hidden menu for a secret commentary by Bill Oakley and Josh Weinstein
Reviews: DVD Talk also has a review of
The Simpsons: The Complete Ninth Season by Ian Jane.