The sideboxes themselves can't be directly moved to the centre column as their structure and the way in which they are generated is slightly different. However the key parts of code behind them can be.

It would need some programming skills, but not at an advanced level, as the code is laready written, just not where you want it. I would recommend creating new pages using EZ-Pages. There is a thread in the forum about inserting PHP into these pages.

You can see how catgories are extracted from the database in includes/modules/sideboxes/categories.php and displayed in includes/templates/template_default/tpl_categories.php and in similarly named files for manufacturers.

However, I would also challenge the premise of your question. Zen Cart is a very powerful system with a lot of facilities to help customers find and purchase products. The site that you are porting is very rudimentary e.g. if I click on Order Now > Browse by Product Type > Watermarked Business Papers, I am presented with 16 pages of very similarly named products. I'd have to know pecisely what I want and be pretty sure that you have it to invest the time trying to find it. Simply replicating this rather than exploring taking the site to a new level feels rather like a missed opportunity.