If you don't mind it being very large (4-9GB), just use
MacTheRipper or
DVDBackup to decrypt the files and store them on your hard drive. You can then use the `Open Folder' option in DVD Player to play the movie. This works fine if you're just time-shifting a DVD temporarily.
If you want to keep the file around, to make a `video jukebox' or the like, then indeed you want to `rip' the DVD to a more highly compressed format (around 1GB for the most common settings). In that case I'd use
Handbrake as your uncle suggested.
And yeah, this probably should be in Applications (where you'd also see the sticky `What application do I use if I need to...'), but you were nice about it