When I try to sharpen in photoshop with smart sharpen or unsharp mask on a separate layer, the preview image looks OK. When I click OK to apply and the sharpening program runs, the image reverts back to its unsharpened state.
What is meant by separate layer?
Obviously, sharpen can only do it's magic on layers containing pixels. So is the layer you're sharpening a duplicate of another layer?
What zoom level are you viewing at when opening the Sharpening filter? The preview windows in the various Sharpen dialog boxes ten to default to 100%, but when you click on OK, you go back to the current view size.