You may be not satisfied with your Ubuntu 11.04 Natty default login screen appearance. You can change it using Ubuntu-Tweak, but it only changes the login screen logo and the background and sometimes Ubuntu-Tweak even doesn’t work.
Here’s a way to launch Appearance Preferences window while at Ubuntu 11.04 login screen, you can change the theme, the background image and the font and see the effect at once.
Open up a terminal window and run this command:
sudo cp /usr/share/applications/gnome-appearance-properties.desktop /usr/share/gdm/autostart/LoginWindow
Log out current session, then you will see this Appearance Preferences window at login screen:
Now, make changes and then login back. Then run this command to remove previous window while at login screen:
sudo unlink /usr/share/gdm/autostart/LoginWindow/gnome-appearance-properties.desktop