hey guys,
first of all please let me tell you that SD DVD NTSC is 720×480, and by the way it make no difference if it would be 4:3 or 16:9, this is just a flag/bit that will be implemented into the MPEG-stream how the aspec-ratio of each pixel must be displayed.
depending on the CS-version that you´re using you need to set menus in different pixel-aspecs, as adobe decided to do some significant changes from CS4 to CS5.
as I haven´t got the NTSC-parameter in mind at the moment (as I´m in PAL-land) I will describe it with PAL. PAL is original 1024×576 for 16:9 in square pixels, if you are working with anamorph pal-pixels this is 720×576 (which is in fact used), but adobe decided to change it to 1050×576.
NTSC is 720x486px, that will be cropped for SD-MPEG2 to 720x480px, but what ever you do, NTSC-DVD could only handle 720×480.
I would advice to transcode assets prior authoring within any DVD/BD-authoring-application. if you are using 16:9-material you should flag it 16:9, so everything should be fine.
cheers
danny