What you need to do is search the web for a convertor, to get the files back
in to avi format, which you can then import in to MM2. If they are
commercial discs, you'll also run in to the problem of copyright protection.
If they are your own discs, then you should be able to extract the vob files
from the dvd quite easily and then convert.
Bear in mind that these files are already well compressed, and any work you
do and then recompressing to put back on a dvd/vcd will only make the
quality worse.
Graham