html:
<div id="wrapper">
<div id="container">all annan kod</div>
<div id="right-advertising">kod</div>
<div class="clear"></div>
</div>
CSS:
body {text-align:left;}
#wrapper {margin:0 auto; width:1230px;}
.clear {clear:both;}
#conatiner {width:980px; float:left;}
#right-advertising {width:250px; float:left;}
Bör fungera.