For NTSC, Open them in VirtualDubMpeg2, resize to 720x480 using Lanczos3 resize algorithm, and crop 60 pixels from the top and from the bottom (this just trims some of the black bar). Save as uncompressed RGB AVI. Then load the AVIs into TMPGEnc (or whatever your favorite MPEG-2 encoder is) and generate as a 16:9 DVD.

The audio is in 2.0 so you'll need to convert to 5.1 if you want it to mesh with the 5.1 of the main movie. Even if you just leave the other channels blank, it'll get the bitrates and file types to match.