1. If you have a movie file for the podcast, you should be able to drag and drop that file into iMovie.
2. A lot of people use
HandBrake for importing DVDs, but it looks like MTR will work too, although I couldn't find the formats into which it will convert files. Once again, a drag and drop should import the movie files just fine.
BTW what version of iMovie do you have, and what kind of Mac?