Howtoforge posted a guide about setting up Kubuntu 10.04 as Linux desktop

This tutorial shows how you can set up a Kubuntu 10.04 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. Kubuntu 10.04 is derived from Ubuntu 10.04 and uses the KDE desktop instead of the GNOME desktop.

  The Perfect Desktop - Kubuntu 10.04