This tweak allows you to switch between any theme within few seconds. You don’t need to restart your springboard everytime you make a change. You should note that DreamBoard is not recommended for iPhone 3G, iPod 2G, or iPod 3G 8GB and it is not compatible with iPad. You can watch the video embedded below to see it in action.
You can download DreamBoard from Cydia under modmyi repo for free of cost. You will need to have a jailbroken iPhone to install this tweak. If you don’t have jailbroken iPhone then you can follow the step by step instructions posted here to jailbreak your iPhone on iOS 4.2.1 with Redsn0w.