#wrapper {width:380px; padding:3px;}

/* begin structure */

#prim {float:left; width:300px; height:200px; margin:1px;}
#second {float:right; width:60px; height:200px; margin:1px;}
#terti {width:370px; clear:both; margin:1px;} 

/* end structure */

* html #terti {margin-left:2px;}