nono your missing it. in winmo we had the same problem and someone made a program that replaced the image with a NON TRANSPARENT image but that image was a "chunk" of the wallpaper.
so it would look "odd" when you slide left and right (the chunk would not line up) but one the core center home screen it would "line up" and be seamless if you cut it right.
so how do I replace the image with ANOTHER image. all I need are its dimensions so I know what "chunk" to remove from the image I am using as a wallpaper.