Wstaw do pliku manufacturer.tpl przed:
{if $products}
{include file="$tpl_dir./product-sort.tpl"}
{include file="$tpl_dir./product-list.tpl" products=$products}
{include file="$tpl_dir./pagination.tpl"}
{else}
<p class="warning">{l s='No products for this manufacturer.'}</p>
{/if}
to:
{$manufacturer->description}
Oczywiście musisz mieć opis przy danym producencie.
pozdrawiam