iPhone Theme Simulator is a dag and drop style program allows you to test and design themes for Winterboard app right on Windows PC or Mac without necessarily having to load and apply.
With iPhone Theme Simulator, you can customize the springboard, lockscreen, Status bar, WiFi ,battery, block, background, time and date, background leads, keys to scroll and more on your jailbroken iPhone. Unfortunately for the moment it is only in Windows version, but a version for MAC is already under construction.