At present, libdvdcss has no release candidate with Debian. I had to install it from source.
Rpm is short for Redhat Package Manager I think. The rpm is only used on Redhat and it's closely asssociated systems, (SuSe, Fedora, the list goes on but I forget what the other rpm distros are...). Debian uses .deb, but the apt-get system automates the installation of .deb files. It is usually
regarded as the top of the linux install systems. There is a program called alienware that is supposed to allow .rpm files to be installed on a debian based system. I have never tried it. I would suggest you download the source and install it. You can find it at