Hi;
Do you want the DVD to be widescreen, or 4:3 ?
I used to have a cam that outputted 640×480, and I still liked to use the NTSC 24p Widescreen .mpg setting, and then did a separate pass for .ac3 audio before using DVD Architect 5.0 for the burn. It seemed to help my Samsung DVD player size the output to widescreen, with a 4:3 video rectangle letter-boxed on my 16:9 TV.
This probably resulted in longer renders and larger files than was needed, but I never overflowed a DVD.