To install Kubuntu 11.04 on Ubuntu 11.04, launch the Terminal and issue this command:
sudo apt-get install kubuntu-desktop
During the installation of Kubuntu, you will be asked to select a default display manager (GDM/KDM), select KDM as a default display manager.
You can then switch between Ubuntu and Kubuntu in the login screen. You have now installed Kubuntu 11.04.
To start it, log out the current Ubuntu session, select KDE Plasma Workspace in the login screen, then log in using your root account:
Screenshot of Kubuntu Desktop:
To switch between KDM and GDM display managers, open the Terminal and run this command:
sudo dpkg-reconfigure gdm
If you prefer a full installation of Kubuntu, run simply this command via the Terminal:
sudo apt-get install kde-full