This really sounds like a difficult workflow, and of course all the conversion and digitizing does not do much good to your signal. Especially usingmastering analog via S-video and then converting analog->DV into Premiere is not really a good idea since you lose a lot of color information and sharpness there.
But your current problem is definitely happening on the Premiere/PC side of things.
What I would suggest to do is to look if you can access your Mac drives from your PC. If yes, you should be able to export your files via reference on your Mac, and open them on your PC if you have the iFinish transcoder installed (maybe using PCMacLan on your PC, depending on if you´re running OSX Panther or not; I think there is a demo versoin avalilable from
Miramar). Then convert it to MPEG2 and burn it to DVD.
Generally it would be best to digitize in 720 mode to avoid the problem that your 640 media has to be blown up to 720. Then try to access a short clip on the Mac from your PC and to convert it using your PC conversion tool. Burn it to DVD and look if this fixes your problems. And you should definitely look if you can set your field order somewhere else on your PC, in Encore or your MPEG2 encoder.
