???? I can watch dvd's that I have bought just fine on my dvd player, and on my computer with the free software that came with it. Could you provide some info as to what problem you are having (causing you to have to buy software).
It's likely that oatmeal is running Linux. There is no licensed software that allows DVD's to be viewed on a Linux-based machine.
This issue is addressed with outgoing MPAA president and CEO Jack Valenti in this interview (which IMO, exposed just how out of touch Valenti really is).
I use XP Home and I don't like the free (or lite) DVD players that come bundled with new computers, they're usually a step above DOS. Full version DVD software costs $50 or more and has a limited scope (what can you do with it? Play Movies. What else? Play Movies)
If you want to use Windows Media Player for DVDs you need to purchase a DVD Pack for $15. This stuff should be included in the OS.
There must be some big money and political ties behind the organizations that control licensing fees.
The same goes for DIVX and other codecs. Give the decoders away for free if you ever want someone to buy your encoders.
I've usually had good results with Xine - nowadays I use the Totem frontend instead the default Xine UI, though, ever since I upgraded to Mandrake 10.
The reason the commercial DVD player software utilities cost money is because the the MPEG-2 decoder licensing fees. That's why the WMP DVD plugin costs money (although I've heard the playback is excellent). Open source software developers tend not to concern themselves with those things, hence why you can get them for free.
WMP is able to piggyback off the codecs of other installed DVD players. You probably got a lite version of PowerDVD, WinDVD or ATI's video-card-bundled DVD player when you bought your computer.
There has been so much trouble over the locked up, proprietary licensing of the DVD format that China is coming out with its own replacement standard, I believe it is to be called "EVD".
If this is released as an open standard, running on the endless supply of cheap Chinese hardware, I can see it eventually replacing DVD altogether.
As far as I understand the situation in the U.S., the DMCA means you can actually be sent to jail for watching a DVD on a Linux computer. How on earth did you let this happen?