Getting commercial (encrypted) DVD's to play in Kubuntu, proved to be somewhat more of a problem than I first envisaged.
You can find any number of web sites that give you clear instructions on what you must do; the priority being to install libdvdcss2, (the value for libdvdcssN is subject to change please ensure you have a current library) which is the library that decodes commercial DVD's. Almost all distributions do not include this, as the legality is open to some speculation. The large film corporations want you to buy DVD's, but are reluctant to let you play them on a computer!
I found that once the appropriate libraries were installed, Kaffeine, the default DVD player, would come up with an error:
(your error may vary on the theme)
The Internet is peppered with this error message, but little appears to be written on how to overcome the problem.
After much head scratching (and cursing) the solution proved to be remarkably simple.
Go into Adept Manager*, the package manager for Kubuntu and install:
The user interface for xine. Goodness knows what it does, but once installed, it lets you play DVD's to your hearts content in both xine and Kaffeine!
* I guess you could also use:
if you prefer the command line.
Hope this helps anyone having this problem and if you're unsure on how to use Adept, please read my contribution on Epson printers, where there is a fuller explanation.