[inebriate]

backup your files before trying this since i am just going off the top of my head...

in products_t.tpl, before {/section}, add </div> and right after {section name=product loop=$products} add:

{if %product.index% is even}
    <div class="shaded">
{else}
    <div class="nonshaded">
{/if}

and in your css style sheet, add (id recommend you change the color values however):

.shaded {
background-color: #654321;
}
.nonshaded {
background-color: #123456;
}