Get Linux: Xubuntu is usable and optimized for speed.

So no Windows, but what else can you install on your PC? Linux! NB: If you don’t know what Linux is, then I think you should read this first: Disadvantages of Using Linux. Xubuntu is a Linux distribution that is optimized for speed. Version 12.04 LTS (April 2012 with Long Term Support) has recently been released. It is based on Debian, a distribution that is known for its focus on security. It runs the XFCE window manager, that is lightweight, but also user friendly. Once you start using it you’ll notice it has a nasty bug that makes the Thunar file manager start up very slowly, but this bug has a well documented workaround (on the FAQ it is question #2) and will hopefully get fixed very soon.