Add following two lines to your /etc/apt/sources.list.
deb http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu jaunty main deb http://ppa.launchpad.net/kubuntu-ppa/staging/ubuntu jaunty main
Execute following command to setup GPG keys and to update your apt package meta data.
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8AC93F7A sudo apt-get update
If you already have previous version of KDE execute following command.
sudo apt-get -y dist-upgrade
If you don't have any KDE version already installed then execute following command.
sudo apt-get -y install kubuntu-desktop