I have PAL DV footage which I need to be viewed with QT / iMovie on Mac. So I have exported using QT Pro. The settings I used in QT to make the mov (after Google research) were H.264, 2000 kbits/sec, keyframe every 24 frames, 2-pass, 25FPS, tried no deinterface as well as with deinterlace. The size is 768x576 because QT resized to this after the Vegas export - size throughout Vegas process was 720x576.
When I am viewing the mov file in a larger window or full screen (> 6 inch high) there is very noticeable horizontal jerky interference or flicker on panning or zooming. It always appears about one third down from the top of the window/screen.
I have checked the original capture as well as the PAL DV output from Vegas and there is no problem.
Have you tried playing the file on a different media player...like say VLC? It could be a player issue and not a file issue. It would be very odd to encode a file and only see an issue in the playback where you say you're seeing it.