Originally Posted by linuxlover.chaitanya
sudo apt-get install kde-full
Or else use Synaptic from System > Administration and install kde-full
package. Search for it.
This will add KDE above Ubuntu's GNOME.
If you want to have 2 separate systems (Ubuntu with GNOME and Kubuntu with KDE), then download installation CD and run separate installation to separate partition. You'll have to choose system to boot during loading.
In this case please note that you'll have 2 grubs on your HDD, but latest installed (Kubuntu) will be the active one.