I used to have the same problem. It’s because you are burning the DVD in a HDV resolution. On any computer or a HDTV it will probably works fine, but on a standard TV (NTSC or PAL) you won’t be able to see the entire footage…try scale down your editing (you can create another sequence and drag your editing sequence in this new sequence) using the NTSC safe box. Now export your video (I use compressor “DVD 90min” preset) and burn on iDVD…