Tom, I'm not exactly sure what you're trying to do, but here's one thought:
1. Create a new layer over your picture (Layer<New Layer<OK)
2. With the new layer active, use the Rectangular marquee tool to draw a
box the size you want.
3. With the marching ants showing, do an Edit<Stroke and specify a certain
number of pixels (maybe 10) and the color black; hit OK and you'll have a
transparent black box.
4. Use the Magic Wand tool set for contiguous and click in the center of
the box; that should select the transparent middle area.
5. Do an Edit<Fill and choose white as your fill color; that will give you
a white box with a black edge on its own layer.
Probably some easier ways to do this that you'll see from others...