First, you need to go into the DVD player's setup menu and make sure that you have the video output set to 16:9 widescreen mode. If you're using the zoom with a widescreen DVD and it's an anamorphic widescreen DVD (check the box for "16:9 Widescreen" or "Enhanced for Widescreen TVs" or Anamorphic), then your DVD player setup is not right. With an anamorphic widescreen DVD and the DVD player set to 16:9 mode, then the image should show on a 16:9 HDTV with no blank space on the side.

With that said, if you're watching any nonwidescreen material on a widescreen TV, then it WILL have those blank spaces on the side, just like watching a widescreen movie on a 4:3 TV will give you those black bars at the top and bottom.. You can't watch what isn't there in the first place. Your alternatives are to watch it that way or stretch the image to cover the full 16:9 screen area, which will look weird.

If you're watching a widescreen DVD and those blank spaces are on the side, then it's probably not an anamorphically enhanced DVD (i.e. it was encoded for a 4:3 TV). Those 4:3 widescreen DVDs are mostly with the first batch of DVD titles and are slowly getting remastered as anamorphic widescreen titles.

With HD DVD, it's the same thing. If the title was originally made with a 4:3 frame, then you'll have blank space on the side. If the title was made in a 16:9 ratio, then it will fill the entire image area. All that HD-DVD will do is run the picture at a higher resolution than DVD.