Connect your PB to the TV. Start the PB, close it immediately. Open it again. NOw the LCD screen stays blank, because the main screen is the TV screen.
This way, you can watch DVD on the TV even with Mac OS X. It's clumsy, but it works.
I was not able to get my Powerbook G4 playing DVD on the TV Screen with OS X 10.1.1 and DVD Player 3.01. it just says "hardware not supported" when TV output is on. Any ideas? With 9.2.2 the same setting works with no problems.