It's a Unix variant. There are multiple distributions. I myself use Ubuntu Linux. It works great. Much safer than MS Windows. No virusses, system freezings, etc. Best thing about it : It's free! You get a system that is imo much better than Windows. The updates for it are also much faster developed by the massive open source community. You get a lot of free software standard installed (Open Office, Firefox, several mediaplayers, chatting programs that can also run MSN, the Gimp (Photoshop kind of program). It's supported by great companies like IBM (they are totally into Eclipse).

But it also has a few flaws, most important : Games. There are not many games on Linux available. You can run several Windows games on Linux but it does not work 'out of the box'. But who cares, I play my games on my PS3. Also the support of Wifi-cards isn't that great. Most of them work, but if you're unlucky you're in for a very technical adventure.

A tip : Most distro's like Ubuntu can be installed next to Windows (you get a dual boot), so you can check it out without losing your Windows installation. By the way, I haven't tried Linux (Yellowdog) on my PS3, I have no need for that.

See www.linux.org or www.ubuntu.org for more info.