Well that's strange because i can customize every MPEG2 profile within Vegas. Is the custom button greyed out when you select any of the mpeg2 profiles? Which version of Vegas are you running?
You won't be able to customize MPEG1 for DVD
This is what i get when i click on "custom" using the Vegas NTSC DVD template. As you can see i've been able to change the framerate & aspect ratio setting and i can change all the other settings if i wish too
