is there a way to switch the window manager from gnome to KDE?
First install KDE. Open a terminal and type:
sudo apt-get install kubuntu-desktop
Then if you logout, when you log back in you'll be given a choice of whether to boot into gnome or KDE.
To make KDE default, open a terminal and type:
sudo dpkg-reconfigure gdm
This will let you pick your default desktop manager.