Well the Operating System is Ubuntu 12.04 x64. How ever the Desktop Enviroment is not the default it is Gnome-Shell. The default Desktop Enviroment for this OS is Unity which means you will need to install Gnome-Shell post install. Then you can download all the theme parts I have listed for this setup. Here are some linx you may find useful to download and install Ubuntu 12.04. I will also include links for burning a ISO image after download as well as links on installing Gnome-Shell. If you are new to Linux I would also suggest you join the forum in the event you need further help with this.
Download and Install Help: [link] ( Note: Once you click this link make sure to choose the architecture of your PC ie. x86 or x64 which means 32bit or 64bit.