hey all - in the SD world there are really only 2 options for outputing 16x9:
NTSC d1 widesceen - 720x486 pixel aspect ratio 1.2
or as square pixels-
NTSC d1 widescreen (square pix) - 864x486 square pixels.
these are the only 2 formats that post facilities will acept as SD 16x9, which is very different than anything HD.
also, keep in mind that field order and interlacing can cause major headaches if you are not careful.