WinterBoard is a very powerful theming tool, created by Saurik (Jay Freeman),used to customize and transform the look and feel of the iPhone & iPod Touch. This application runs in the background and handles everything from basic SpringBoard themes (Wallpaper, Dock, StatusBar, & Icons) all the way up to complete themes that customize the entire system UI (Buttons, Backgrounds, & Sounds). WinterBoard also has the ability to theme individual applications which are usually referred to as App Themes.
How To Install WinterBoard Themes On iPhone, iPad And iPod Touch