Follow the instructions on this page to install the ubuntume-artwork package.
You have to log out to finish the installation.

The ubuntume-artwork package installs custom:

• GRUB picture (/boot/grub/splashimages/grub/medine_moon_right_below.xpm.gz)

• usplash

• GDM login screen (/usr/share/gdm/themes/UbuntuME)

To change this screen, use the “System→Administration→Login Window” menu.

• GDM splash screen

If the splash screen is not set after the installation of the ubuntume-artwork package, execute the following command in a terminal window:

gconftool-2 --type string --set /apps/gnome-session/options/splash_image "/usr/share/gdm/themes/UbuntuME/ubuntume-splash.png"

• Wallpaper (/usr/share/ubuntume-artwork/ubuntuME.jpg)

If the wallpaper is not set after the installation of the ubuntume-artwork package, execute the following commands in a terminal window:

gconftool-2 --type string --set /desktop/gnome/background/picture_filename "/usr/share/ubuntume-artwork/ubuntuME.jpg"
gconftool-2 --type string --set /desktop/gnome/background/picture_options "stretched"

Other wallpapers (used by the screensaver) (/usr/share/backgrounds):

...

• GTK, Metacity and icon themes

If the theme is not set after the ubuntume-artwork package installation, execute the following commands in a terminal window:

gconftool-2 --type string --set /desktop/gnome/interface/gtk_theme "HumanME"
gconftool-2 --type string --set /apps/metacity/general/theme "HumanME"
gconftool-2 --type string --set /desktop/gnome/interface/icon_theme "HumanME-green"

• Firefox toolbar

• Login sound (changed to /usr/share/sounds/tasmiyah2.wav)