The MPAA (Motion Picture Association of America) is trying to basically gag everyone and anyone involved in trying to use DVDs and DVD-related material in a way that they never intended.
DeCSS (Content Scrambling System) is an algorithm intended to unscramble DVD content. You see, the movie files are readily copiable from a DVD disc...but you can't actually read them on a computer because they're encrypted. DeCSS is the algorithm which, when used properly, can allow you to decode the MPEG (Motion Picture Experts Group - basically it's a movie format) movie data off a DVD disc and do what you want with it.
This means bad things to the MPAA, because they think that this will immediately permit people to do to DVDs what Napster and MP3s did for CD audio. Of course, you don't see the music industry suffering, but that's neither here nor there.
DeCSS has practical uses. It was originally developed as a component that later led to a Linux DVD player application, which, up until that point, was not available. The information used in DeCSS was obtained from a buggy Windows-based DVD player made by the Xing corporation. The author originally used it to develop DVD decoding software for Linux, but then the MPAA sued him for violations of the DMCA (Digital Millenium Copyright Act), because, according to the DMCA, it is illegal to create, possess, or provide others with tools or the means to circumvent an access control measure.
So, you see, this puts a strangehold on anyone who wants to watch DVD movies on any system other than Windows, because no such software exists...Furthermore, it is unlikely that it would ever exist, since those operating systems are considered "fringe markets" by corporations, and not profitable enough to warrant their resources.
The backlash resulting recently against the MPAA is people using DeCSS in forms of art and depiction, basically claiming that computer code is a conversation of ideas, and thus should be protected under Freedom of Speech. In this vein, people have been broadcasting the code (Spoken aloud) over TV and radio, printing it on T-shirts, embedding it in graphic images, and obscuring it in other ways, so that it is available, if not useable. Basically, if someone had a lot of free time, they could try to transcribe all the code into a compiler and then work with it there. The MPAA has a big problem with this, of course, and as a result has been trying to squash a lot of people by threatening their ISPs and whatnot if they post any information related to DeCSS. They sued
2600 Magazine for violations of the DMCA for simply LINKING to pages where it could either be found directly, or searched for.
Alright...I'm off my soapbox now. :-)