If it's already in mp4 format, it's fastest in QT Pro - you just trim the movie to each episode and then Export and set the audio and video settings as 'Passthrough'.
If you don't have (or don't want to pay for) QT Pro, then MPEG Streamclip will do the job, but the exporting will take longer and it will lose a little quality as it's being recoded.
By far the easiest way to do what you want is to Handbrake it from the start episode by episode (use the queue function) - either each will be a separate title on the dvd, or count up the number of chapters in each episode.