<{if $block.title=="block-name"}>
<div class="thisclass">
<{elseif $block.title=="blockname"}>
<div class="anotherclass">
<{/if}>
<{if $block.title=="block-name"}>
<div class="thisclass">
<{elseif $block.title=="blockname"}>
<div class="anotherclass">
<{/if}>
<{assign var=zaehler value=1}>
<{foreach from=$photos item=photo}>
<{assign var=zaehler value=$zaehler+1}>
<{if $zaehler % 3 == 0}>
YOUR BANNER
<{/if}>
<{/foreach}>