you need encryption code on linux for viewing encrypted dvd's that you own.....
( most commercial dvd's like films etcetera )

this capability is not included by default in linux.

below, website to get most recent versions, and small instruction.

website:
http://www.videolan.org/developers/libdvdcss.html

from Packman:
_______________________
 Now, the new copyright in germany is coming into force, it's no longer allowed to provide tools to breake technical protections. Therefore we can no longer provide libdvdcss, sorry. 

To give you the capability to watch your own, paid-for DVD's on linux systems, we want make you the installation as easy as possible. 

Download the libdvdcss tar.bz2-file in the same version as the nosrc.rpm from videolan , copy it to /usr/src/packages/SOURCES/, download the nosrc.rpm and compile the library using :

# rpmbuild --rebuild libdvdcss*.nosrc.rpm . 

The final RPM's you can find in 
/usr/src/packages/RPMS/i586/ 
or 
/usr/src/packages/RPMS/x86_64/, 

you can install it like every other RPM. 
 
_____________________
EOF Packman.