A few days ago one of my colleagues showed me this interesting tutorial on how to use a single image as a sprite map to skin an entire application. The idea isn’t new at all, desktop applications use it a lot to change their appearances.
Basically, you have a single large image that contains graphical elements used by the controls of the application. You read the image and extract those graphical elements (bitmap images). This Flash tutorial shows you just how you could do it in Flash: http://flash.tutsplus.com/tutorials/effects/build-a-smart-flash-decalsheet-system/. This is quite interesting and worth going through.