Duplicate the layer twice.
Disable the bottom (original) layer (poke it in the eye).
Rectangular marquee select the left side on the middle layer, expand it 1 pixel, and delete the selected pixels. Rename the layer RIGHT SIDE.
Inverse the selection, expand it 2 pixels, and delete the selected pixels. Rename the layer LEFT SIDE.
Jim Kanter,
Digital Film Institute
http://www.dfilminst.com