You won't be able to use the DVD as a source in the same way as a DV unit. You'll have to rip either the whole movie or part of it and then import the exported file into your video editor.
There should be something you can use here:
But I don't know if any of them let you bypass the copy protection if the DVD has any. I'll look into it, but I'm sure someone else has better advice on this than I can give. I'm sure Jixby would know.