Well fer starters you're going to be editing skin1/customer/main/products.tpl or products_t.tpl files.
In there you will see the call to the thumbnails, it's an include statement. You can either manually set the "x" and "y" - width and height - in that include statement or stick with configuring the width in xcart and having it do it proportionally.
It looks to me as if the site you like is using a 120 width thumbnail configured the regular way through the x-cart backend.
As far as the layout, it is upto you to edit the html code appropriately to make the thumbnail show up next to the description, moving the price and "see details" verbiage below that.
Something like <tr><td><img tag></td><td>description</td></tr> blah blah blah....