You don't need to Remove your gnome 3 desktop or your nautilus file browser.
How to Run KDE Plasma Widgets in Ubuntu Gnome3
Add Plasma Widgets to Ubuntu 11.04
Just install plasma-desktop and start it!!
How to install plasma Desktop
sudo apt-get install plasma-desktop plasma-scriptengine-python
How to start plasma DesktopYou can start it by entering the following command
hit Alt + F2
When you start the plasma desktop for the first time, the default KDE panel will be on it you can remove it if you don't want it by right click, remove this panel