<style type="text/css">
	.clear { clear: both; }

	#wrap-advert {
		width: 960px;
		margin: 20px auto;
	}

	.advert {
		width: 300px;
		float: left;
		text-align: center;
		margin: 0 10px;
	}
</style>

<div class="clear"></div>
<div id="wrap-advert">
	<div class="advert">
		<!-- advert code goes here -->1
	</div>
	<div class="advert">
		<!-- advert code goes here -->2
	</div>
	<div class="advert">
		<!-- advert code goes here -->3
	</div>
	<div class="clear"></div>
</div>
<div class="clear"></div>