Installation:
Choose from one of the 20 wallpapers and download the .zip file. They should be named 1.dds, 2.dds, etc. You can extract it from the .zip folder if you want, but that is not required. You drag the .dds file into the folder objects (skyrim -> data -> textures -> interface -> objects). There is another .dds file in that folder called "mainmenuwallpaper.dds". Your next step is to rename your .dds to "mainmenuwallpaper.dds" and remove the old one.
Enjoy!
-Original Mod
High-Res Wallpapers