You still cannot easily play dvd's on free software Linux distributions... sadly...

But those guys describe it nicely how to do it with the medibuntu repository - only for Hardy. For Intrepid, the command must be slightly changed (and I prefer aptitude, as it also keeps a log of what it does)

So, as root, do:

 
wget http://www.medibuntu.org/sources.list.d/intrepid.list -O /etc/apt/sources.list.d/medibuntu.list 
aptitude update 
aptitude install medibuntu-keyring
aptitude update
aptitude install libdvdcss2 w32codecs