Those are because of interlacing. Do you mean when you take screenshots in your NLE because if so (well if it is Vegas anyway) if you go to the movie properties and make the footage deinterlaced you can take save screenshots without those lines.
If you take your frame into photoshop and use the filter/video/deinterlace it will correct this problem for stills. These are not a probem when watching on an NTSC monitor. hope this helps.
In that case - You have got your interlaced fields in reverse order and the video is playing the wrong field first. (Its a time thing and what you are seeing is a fraction of a second later being played a fraction of a second ahead of itself- does that make sense ? :-/)