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 file!
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
The only SD files that Premiere likes are DV AVI type 2