Install the theme as usual, with the login manager or manually, but I suggest a little trick.
Change the background (Background tab in Login Manager, or manually in /etc/kde#/kdm/backgroundrc) to the "base-background.jpg" in the theme folder. Set the Position to Scale & Crop.
This way you'll get a smooth transition (your screen won't turn black or change to the def. bg) between the login screen and your desktop.
The default resolution of the theme is 1280x1024, but in the attached Image Pack, there are backgrounds in 1440x900 and in 1600x1200. Just copy and rename the desired images to the theme dir, overwriting the default ones.