Are you dropping the ProRes 1280×720 file into DVDSP? You need to take it to Compressor and encode it for DVD first – you get two files, m2v and ac3. I’m guessing if you’re dropping this ProRes file into DVDSP, the aspect ratio in the intermediate conversion DVDSP tries to do isn’t working out – going from square pixels to nonsquare, and all that junk. That’s not the way to do it – when you put files into DVDSP, you should see green dots almost immediately, not yellow 🙂
You definitely don’t need two versions.