Not sure if this is exactly what you wanted, but this is what I did in Paint Shop Pro:
1. Create a fine grid and make sure objects will snap to it.
2. Create a new, blank layer above the original.
3. With the brush tool (or whatever the PS equivalent is) begin to trace the lines of the underlying image. What you should see happening is the lines you draw "snapping" to the grid, making them almost all vertical or horizontal (like Etch-a-Sketch). Make the lines a dark greyish colour.
4. Once you have finished tracing the lines, fill the bottom layer with colour (this will be the grey-brown of the Etch-a-Sketch background).
5. To make it look more realisitc, I added a bit of texture to the background, added reflection, and gave the lines some highlight and shadow. I also borrowed somebody's drawing of an Etch-aSketch to use as a border.
Here is an original photgraph that I took:
http://www.dpchallenge.com/image.php?IMAGE_ID=7027
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And here is the same picture in Etch-a-Sketch style:
If target=_blank>http://www.dpchallenge.com/image.php?IMAGE_ID=7168
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If
you are interested, I will give you more details on how I made the image. If there is not an equivalent method of doing this in Photoshop, I would happily convert some pictures for you.