This is an old issue that I finally found the solution to. When moving from
8.04 to 9.04 I lost the ability to watch DVD movies, but got it working again
after the fix below.

Found it here, where someone commented on a very old thread:
www.ubuntugeek.com/...ncrypted-dvds-in-ubuntu.html

Fix:
This doesn't work for me (Ubuntu 9.04). I just discovered the new version
(libdvdread4) is in the Restricted Extras package, which means from this release
on you should tell your terminal to do THIS:

sudo /usr/share/doc/libdvdread4/install-css.sh