Format doesn’t matter on the computer. There are ways to convert, but it can be problematical.
If you want to try, the easiest method is to use FAVC. You’ll need Net 2.0 and AviSynth installed first, but they are free and there are links to them at the FAVC site. http://favcfavc.googlepages.com/
FAVC says it can now import vob files straight from your movie. But I might use Vob2Mpeg first to get it into mpeg2 form first. http://www.videohelp.com/tools/VOB2MPG
Once imported to FAVC, use the HC encoder that is included and set your output to NTSC. Let it reencode the movie.
You lose the original menus doing this, but you can make a new, simple menu in FAVC and put in chapter points as well, though you can only go by time sections and cannot set them exactly where you might want to.