I am really not sure what is going on in your case but I can tell you that until I sorted it all out I also got the jerky/jumpy images. Shame on me as I am originally from Europe, but I only "think" PAL is also lower field first... I'm not sure. So the method I described should be the same for you, can you confirm that PAL is lower first?

Also, I don't quite understand where in the DVD authoring process you have to set field order, unless you encode your footage in the DVD authoring program itself. The way I told you, you should already have the video files encoded to MPEG2 when importing them into the authoring software, so a new encode is not necessary.