How can I install GNOME desktop over Kubuntu 11.1?
Open up a Konsole (Menu -> System -> Console) and enter the following command:
sudo apt-get update && sudo apt-get install ubuntu-desktop
You will then be prompted to confirm you want to initiate the installation, enter "Y". You'll have an option to chose your display manager, chose GDM. Then, once complete - Log out and log back in!
Alternatively you may use Synaptic and search for "ubuntu-desktop".