There are of course (silly) IP problems with DVD encryption/decryption. You may well find that your multimedia player refuses to open discs, and/or gives errors like this when you run it from the command line:
main input error: ES_OUT_RESET_PCR called
Open source systems like Linux get around these by various means that mean a bit of hassle for you, the poor end user. I hope these instructions make fixing the problem straightforward for you.
First, install Ubuntu Restricted Extras:
sudo aptitude install ubuntu-restricted-extras
Then run the DVD decryption installation script:
Now you should be able to drop in and play a DVD.