You have to step back from how it looks, as it's done rather differently.

There are no images needed down the side, those can be done by simple left and right borders in css.

The image at the top would consist of the the curves and the left hand dot.

The right hand dot is in a variable location depending on the width of the header, so would need to form part of a background to the header.

The imagery at the bottom would be the background to the boxes supplementary links. Zen Cart doesn't have that feature, so you would need to edit each of the listing box templates to add this or something similar and then hook the bottom background to that.

I have to say though, that this would require some moderately advanced CSS skills to get everything pixel perfect and working properly in all browsers.