Ubuntu is a linux distribution, a very popular one. As open source Ubuntu is free, you can find it on cover mounted dvd on magazines, you can download it from the internet and burn a dvd to install from, you can also buy versions of it - so on a cd or dvd because you don't have adsl or with printed manuals and so on, you're paying for someone else to have put in onto media, stick it in a box and post it to you - not the OS itself. <download for free from here - http://www.ubuntu.com/ >

Some variants of linux can also be bought with support from a company for example redhat - means you pay for the distro but have the chance to pick up the phone and get help if things go pear shaped.....

Personally I use Suse but I've considered swithcing to ubuntu or mandriva just to see what they're like. Each distro has it's own little quirks and different set up out of the box.

----------

Toolset: Blender, GIMP, Indigo Render, LuxRender, TopMod, Knotplot, Ivy Gen, Plant Studio.