DVDxDV is very straightforward to use, but costs $25. It can export to DV or unompressed if you need to do further editing in FCP.
ffmpegx is a little more complex to use, but can be used for free - although they ask for a $15 shareware registration if you like it. It has a wealth of export format options.
Handbrake is both easy to use and free! But it has a fairly limited choice of export options, which may not help you, e.g. if you want to edit the video in FCP.
If the DVD is not copy-protected then you should just be able to work directly from it (or copy the VIDEO_TS folder on to your hard drive and work from that). Otherwise you would need to use something like
Mac The Ripper to rip the DVD to your hard drive first.