How did you convert those analog tapes to digital files on a DVD... and what codec are those DVD files?
Read Bill Hunt on a file type as WRAPPER http://forums.adobe.com/thread/440037
What is a CODEC... a Primer http://forums.adobe.com/thread/546811
What CODEC is INSIDE that file? http://forums.adobe.com/thread/440037
Report back with the codec details of your file, use the programs below
For Mac http://mediainfo.massanti.com/
Once you know exactly what it is you are editing, report back with that information... and your project setting, and if there is a red line above the video in the timeline, which indicates a mismatch between video and project