This tutorial shows how you can set up an Ubuntu 9.10 (Karmic Koala) desktop that is a full-fledged replacement for a Windows desktop, i.e. that has all the software that people need to do the things they do on their Windows desktops. The advantages are clear: you get a secure system without DRM restrictions that works even on old hardware, and the best thing is: all software comes free of charge.

http://www.howtoforge.com/the-perfect-desktop-ubuntu-9.10-karmic-koala