Like Mike I am assuming that the material you are trying to edit is a VOB file and that the problem you are encountering is that the Video and Audio have lost synchronisation?
This is a well known problem, here I am quoting from the FAQ of a alternative MPEG editor, at..
http://womble.com/support/FAQ09.html
" 6. Since the editor is single file based, and since the DVD file system breaks one continuous movie stream into multiple 1 GB segments, this introduces video and audio discontinuities when loaded by the editor as consecutive clips. Those discontinuities may exhibit as loss of video for a maximum of one GOP (about half of a second) and as loss of audio for a maximum of two encoded sound frames (about 50 to 60 milliseconds). Worse still, this frequently destroys the original synchronization between video and audio. To work around this problem, it is always better to read the DVD disc into the computer as one single file by setting the "No splitting" option in a DVD reader."
One solution is to re-transfer the VOB useing DVD Decrypter available free from...
http://www.dvddecrypter.org.uk/
to produce a new copy of the material after first going into Tools, Settings, File Mode of DVD Decrypter and setting file splitting to "None"
This should produce a editable version that is in sync.
Alternatively I think you can do a similar job using the free version of DVD Fab?