This patch is a Gnome login screen theme that looks exactly like Mac OS X Leopard's login screen.
Install it the same way as you installed the Mac4Lin GDM theme in the guide. That is,
Download the file "UbuntuLeopard_GDM_theme.tar.gz":
Open "System" -> "Administration" -> "Login Window"
Under the "Local" tab, click the "Add" button, next to the theme selector.
Find the file you just downloaded and click "Install"
Enjoy that awesome Leopard look!