Just in case you haven't come across them before, the site to try first (IMHO) is http://www.videohelp.com/tools?s=23#23
This is a fairly comprehensive list of video manipulation tools available under Linux.
For ripping a DVD and making a backup copy you can use DVD::RIP http://www.exit1.org/dvdrip/
For general video editing then Cinelerra http://heroinewarrior.com/cinelerra.php3 takes some beating (and I can run it on my 1.2GHz/512Mb RAM Athlon system without any problems).
For authoring your own DVDs then you can use 'Q DVD Author' http://qdvdauthor.sourceforge.net/
Another good alternative is DVDStyler http://dvdstyler.sourceforge.net/index.html
There are plenty of other links at VideoHelp as well
