Navigate to var/root/library/summerboard (or something close to that). Then drop in a folder that is named the theme name. In that folder have Dock.png, Wallpaper.png, MiniDock.png, and I believe it's StatusBar.png but that one could be wrong. Then have another folder in there named Icons.png. Then name the icons what shows underneath them in the springboard. Text.png, Phone.png, Mail.png, etc.
Found
here