What you need for playing dvd's is "libdvdcss". It is on the plf repository, so if you don't have that set up, go to http://easyurpmi.zarb.org/
and set up all your sources. Of course you will need "plf" for tha good stuff, "contrib" to back up dependancies in plf and "update" just cause you do, and "main" cause you don't have your cd's. That just leaves "jpackages" so may as well have em all eh.
Fire up your Mandrake Control Center and choose "software management". Now choose "Select from where software packages are downloaded when updating the system". Leave an 'x' in all the boxes exept the ones that indicate they are 'cd's', and it will not ask you for cd's again unless you go back and select them. It will now use the sources you installed from "easy urpmi". This is all good, my system was setup from an ftp install so I never did have cd's even for install and it is a very happy computer.
Hope this is of some help, time for bed.
P.S. just checked to see if anyone posted since I started my answer, got sidetracked and found my way back to pc, do as apimente.br suggested and check out that thread, Motub put alot of effort into some good info there plus more.