I take it no error meassages,
Try running from a terminal, ie in a terminal
type vlc and then load a dvd, once it crashes post the
error messages here. There are lots of reasons apart from codecs,
that cause this problem, video drivers, and dma settings to name
a couple.

i got mine working by going to
ubuntu help centre
option music, video and photos
2.1 playing videos and follow instructions
worked for me

How to play video dvd in ubuntu 9.10 karmic
Koala<blog.dipinkrishna.info/.../how-to-play-dvd-in-ubuntu-910-karmic\
.html>
blog.dipinkrishna.info/.../how-to-play-dvd-in-ubuntu-910-karmic.html

This is fairly basic but it is worth a try.