DVD's aren't terribly high quality to begin with. (5-8Mbps). It can also matter what codec you rip the DVD into when making a mov. If going to FCPX I would use ProRes.
I use MPEG Streamclip for DVD ripping. It's free.
http://www.squared5.com
Ryan Holmes
http://www.ryanholmes.me
vimeo.com/ryanholmes