<<<but your best results would come from going back to your source material, not converting an exiting DVD. >>>
I'm with him. Far better results going back to the original clips and convert to PAL either with Compressor or Nattress and/or Photoshop. Then re-author. We are in the middle of a request to convert several of our production demo reels to PAL. We're sending out a massive DigiBeta tape with all the original uncompressed clips. Convert to a PAL tape. Call me if you have a problem.
Every compression damages the image. First damage happens when you made the DVD(1). Then you have to de-compress the work(2). Then you have to convert it to PAL(3). Then you have to make the new PAL DVD(4). I'll be surprised if the show didn't look like fuzzy, stuttery garbage by the time you got done. And that's assuming a perfect, professional, uncompressed, non-DV show in the beginning. If you started out DV, then all those numbers increase by one since DV started out compessed and slightly damaged right in the camera.
A DVD isn't a "thing" like you think. Yes, it's one silvery video disk, but inside, it's a traffic cop or bookkeeper. "If the user clicks on this, do that. If the user wants the Extended Director's Cut, then play this.
Each "this", "that", splash screen, graphic, movie, clip and text display has to be individually converted to PAL. The opening screen that you spent days composing will need to be resized for a PAL disk. Their frame size is different. Each navagation screen and button will be slightly off.
<<<convert my ntsc DVD to a pal DVD>>>
So the short answer is no.
Call them.
Koz