Based on reading a LOT of problem reports, importing files from a DVD camcorder or other MPEG device, or Ripping DVD files rarely results in success in Premiere... do not be fooled by movie industry advertising into thinking that "DVD Quality Video" is suitable for EDITING... it is not... a DVD is designed to be for PLAYBACK only... and that includes trying to edit a Standard Def MPEG or VOB file!
You should also use WAV sound files, not the compressed MP3 format, To work with AC3 files in Premiere, it MAY work to copy the ad2ac3dec.dll file from the Encore DVD directory into the Premiere directory
Go to my notes page http://www.pacifier.com/~jtsmith/ADOBE.HTM
Click the internal link for editing compressed files... read
There are other products better suited to your task... but if you only have DVD type files, you should convert to DV AVI... go to the VideoHelp link in my notes and look for a program to convert... but do be aware that converting from a HIGHLY compressed viewing format back to an editing format is going to cause a drop in quality
The only SD (Standard Def) files that Premiere really likes are DV AVI type 2