To move a selection you can use this tool , it does a pretty fair job. It can be found in the Tools window.
In the bottom left corner of your Layers window there is a button, Add a New Layer. It will add a new layer on top of all the others. The blue up and down arrows will move the selected layers either up or down. Use them to move your background to the background of your image. Use them to move the middel ground to the middle ground of and image. And use them to move the foreground to the foreground of the image. If they are all contained in seperate layers that is.
Hope that helps.
:wink: