Well both of these can indeed be customized. However, I think that creloaded (an oscommerce based improvement) is actually easier to customize than either of them.

What exactly do you need customized the code or the layout? These are different items entirely with the layout and look being the easiest to accomplish.
shows how to do you layout.

You will need to know php and html to do this.
Just check the oscommerce live sites for samples there are several there that have been customized.

There are even template sites that built prebuilt customizable templates for all of these. So you might find one that has what you are looking to do.