First off, I suggest that you forget about the Filter>Sharpen, command and it's relatives Sharpen More, and Sharpen Edges. Filter>Sharpen>Unsharp Mask is the bread and butter of sharpening. If you haven't sat down and gotten familiar with this tool yet, do so now and your efforts will be rewarded many times over.
I've been using the following method of sharpening with a layer for a number of years. Here's how it goes.
- duplicate the image to a new layer by dragging the background layer to the "new" icon at the bottom of the layer palette
- use Filter>Other>High Pass with a radius of about 1.6 - you'll want to experiment with this value later.
- set the mode of the layer to Overlay
- voila! Your image is sharpened.
Here are some of the advantages of this method of sharpening.
You can erase parts of your new sharpen layer to get rid of artifacts, wrinkles, etc, that show up after the sharpening.
You haven't changed your original image, and can go back in time by deleting and recreating the sharpen layer.
BTW- I've enclosed an atn file for Photoshop folks. To use it, save the attachment, click on the menu button in the Actions palette, select the Load Actions command, and load the .atn file from the location you saved it to.