It could be a couple of things, depending on where the DVD came from and how you're viewing it.
Are you watching it played on your timeline? If so, is there a red line above the clip on your timeline? If so, press the Enter key so that the video is rendered (the red line will turn green), then it should play smoothly.
Also, if you're using DVD video in a project, make sure you're using the DVD project preset. Otherwise, your final video output will play jiggly. (It's an interlacing issue.)
PrE can Import and edit 100% DVD-compliant (very important) .VOB's. However, if they are not 100% DVD-compliant, then problems can arise.
Take a look at this ARTICLE for more background on editing .VOB's.
For the moment, I am going to take another approach to the issue that you presented. I could be wrong, but I would like to rule it in or out.
By any chance, did you decide that you wanted a better look at the Timeline frames and decided to expand the Timeline? But, you did not do that using the slider above the Timeline, but rather used the Time Stretch Tool or some other means to increase the duration/length of the video on the Timeline?
Decreasing the duration of the Timeline video will speed up the action, whereas increasing the duration of the Timeline video will give you slow motion and, if you do not click Maintain Audio Pitch in the Time Stretch dialog, distorted audio.
In your case, was the audio distorted as well as the video in slow motion?
This can happen when you timestretch the clip. Or if you have interpretted that footage at a different FPS (Frames per second).
I would suggest that you select the clip in the Project view and Rightclick on it to choose the "Interpret Footage" option. From this option, you choose a 29.97 FPS for this clip and check if dragging this clip to the timeline does the trick for you.