Hi,
A quick google search suggests you need the RPM with libdvdcss, which can be found with instructions for xine here: http://cambuca.ldhs.cetuc.puc-rio.br/xine/
Once libdvdcss is installed, other movie players should understand it too.
I think the reason it wasn't installed should be pointed out. The code for decoding encrypted DVDs (as some are not encrypted, most are, but not all), is closed source and has to be licensed for use. So hence, I believe (and correct me if I'm wrong) that this code is not official and probably illegal to run.
Just pointing this out.
Cheers
Dave