Start by making a duplicate layer of the BACKGROUND LAYER. Now turn the "eye" of the background layer off, as you see in the screenshot. If we merge the three top layers together, we will end up with what we want: a top layer that has been sharpened and the never sharpened background layer. As you will see on the next screenshot, the LAYERS Palette has a command "MERGE VISIBLE" that will accomplish this task easily.

The "MERGE VISIBLE" command is found in a "fly-out" menu. To access this, click on the little triangle that is in the upper right hand corner of the Layer's Palette. The next screen shot shows what is on this "fly-out" menu.