So log in your Ubuntu and go to System -> Administration -> Software Sources. Here you will be asked for your password. Go to the Third-Party Software tab, click the Add button and type the following line: deb http://ppa.launchpad.net/kubuntu-members-kde4/ubuntu intrepid mainand click the Add Source button. Next click the Close button. You will be prompted that available software is out of date. Click the Reload button and wait for a while for your repositories to be updated. Now open a terminal by going to Applications -> Accessories -> Terminal and type in: sudo aptitude update && sudo aptitude install kubuntu-kde4-desktop Supply your password and press Y when asked if you want to continue. When all packages have been downloaded you will be prompted to configure kdm, KDE's graphical login manager. Press Enter.
And here it is KDE4. Play around with it and see how it looks. If you later decide to uninstall KDE, open a terminal through Gnome and type:
sudo aptitude remove kubuntu-kde4-desktop