I use Handbrake on a PC to rip the source, which sometimes needs trimming in Quicktime 7 Pro (not sure if you can still get this) to make the file manageable (Handbrake can only select down to Chapter level, which is stupid if all you need is 3 seconds). Then transfer to Mac to edit in iMovie.
It's laborious, but necessary to get the picture quality IMO.
I love iMovie (mostly) *hugs software*