Step 1: Choose An Image
First select an image. I will be using this image:

Step 2: New Raster Layer
Create a new raster layer. Layers >> New Raster Layer.
Step 3: Fill With Gradient
Fill the new raster layer by selecting the gradient that comes with PSP called Black-White.

Step 4: Edit Gradeint Layer
Select the gradient layer and double click to edit options. Change the blend mode to Burn.

Step 5: Duplicate The Background
Duplicate the orignial image and drag it to the top or paste the original image as a new layer (cntrl+L).
Step 6: Adjust Layer
Select the top layer which is the duplicate of the original. Change the blend mode to Overlay.

Step 7: Merge & Done
Merge All Layers. Layers >> Merge >> Merge All. Viola!
From Shalane's personal site.