There are so many steps along the way where this can be determined or switched. That camera can record in both 16:9 and 4:3, so make sure the camera is set to 16:9 widescreen. In Vegas make sure you create a widescreen project. Make sure you use the appropriate widescreen rendering template when generating the MPEG2 file. In DVD Architect set the project type to widescreen there as well.
And, your DVD player and TV will both have options to override what the DVD says and play it as either 16:9 or 4:3, but they should both default to the settings in on the DVD.