choppy footage when after put in time line

I am trying to make a demo reel from ripped footage from a dvd of my acting scenes from a show, but once I drop the footage into the time line it goes choppy and inconsistent. I can import the footage and watch it in the left screen and it is fine. Even after I render the work it is still in this choppy way. I have edited with raw footage from my cmera many times and never encountered this problem. I can't figure out why it all of a sudden goes this way. Please help.
The footage is in mpeg format.