Try the Lite-On tab of the booktype dialog, as it seems it could be a Lite-On burner. Also get better media, such as Verbatim or Taiyo Yuden blanks, or at least burn at a slower speed with your current :& media.
Are you sure you're burning DVD-Video content (i.e. VIDEO_TS folder/IFO/BUP/VOB files)? If you're burning AVI/WMV/etc files, you'll need to convert them with a program like DVD Flick before burning, or the disc won't play on the majority of the DVD players.