The subject pretty much says it all... the source video is 50hz interlaced PAL MPEG-2 ripped from a region 2 PAL DVD. The desired outcome is a region-free NTSC DVD. The DVD authoring app of choice is DVD Movie Factory 3.

Alternatively, can DMF3 author a DVD with some PAL-ish (720x540, 50hz) tracks and some NTSC-ish (720 x 480, 59.94hz) tracks (assuming, of course, that the DVD player itself won't freak out and can handle it)?