now that you've used mactheriper to rip the dvd, you can drag the ripped .vob files (in the video_ts folder) into mpegstreamclip. that'll let you set in and out points for your clips, and then you can export them to a variety of formats.
it takes some experimenting to get the hang of it, but once you do, it's pretty easy. i usually set in and out points for the clip, trim it, and then save a copy of the clipped .vob file, so that i've got the clip in the best format i can get it in (not re-recompressed); then i export it to whatever i need it for. though usually for teaching purposes, i just replay the .vob clips back in vlc player.