Here is where you will find it:
http://xubuntu.org/

Xubuntu is a variety of the Ubuntu Linux distribution, http://www.ubuntu.com/ , but centered around the lightweight Xfce-desktop( http://www.xfce.org/ ). The benefit of using Xfce instead of Ubuntus own Unity-desktop or the dominating Gnome-desktop, or KDE, is that you still get a modern looking and functional desktop but without wasting unnecessary computing power just running it. For one, it benefits the framerates in modern Windows-games which run just fine under Wine in Linux. More exciting stuff will come out of that as Valve soon will be launching a Linux-native gaming client for Steam, Valves popular online game store/repository.
A low resource desktop will also keep the computer cooler and more silent running, as fans don’t have to spin up as often just manouevering the desktop. They can save themselves until there is a demanding and interesting task for the cpu/gpu to crunch through.
Now, there is other lightweight desktops around like Lxde or Openbox, but Xfce is much more polished and feature complete rendering it no big sacrifice to not be running ie Gnome itself. Personally I believe that Ubuntu itself is already the best Linux-distro around, or rather Debian is – on which Ubuntu is based, but Ubuntu add all those preconfigured little things that makes just setting up the computer not a pain. And Xubuntu is Ubuntu, but without wasting resources, an almost perfect Linux-distro imho and I can wholeheartedly recommend Xubuntu for anyone deciding to switch over to Linux. And for seasoned veterans as well, for that matter.
Of course, this site is running off Xubuntu! Why not a Linux server-distro powering the site, even less demanding on resources, you may ask? Well, this is not only a server, this is my Linux play-box which happens to run a server as well. And since the server itself is no big project of mine, it just exists, it can happily be alive in the background on my Xubuntu-box
I added some Xubuntu-identifiers to the header so no one can miss out on what’s the deal here
And for those who don’t even know what Linux is(!), do try to get the background here:
http://en.wikipedia.org/wiki/Linux
(Wikipedia ftw!)
And, in case you didn’t know it, all your shiny new Android-cellphones and Tablets are running Linux too! Your 55″ Smart-TV:s as well. And Apples IphoneOS and OSX are in large parts based on the Gnu Operating System, on which all Linux-distributions are based, even though Apple uses a BSD-kernel instead of a Linux-kernel(very much alike, both are *NIX)! And what do you think the mighty Googles servers are running? Not Windows, eh?
Inventor of Linux(Linus Torvalds):

“Linux”(or Tux)

The latest Linux “kernel”:
http://kernel.org/
Free software(as in speech, not as in beer):
http://www.gnu.org/

Founder of gnu, and the Free Software Foundation:

Richard Stallman;
http://www.fsf.org/