#nav    {
	background-image: url("media/botones/fondo_btn.jpg");
	background-repeat: no-repeat;
	position: absolute;
	top: 63px;
	left: 260px;
	width: 510px;
	height: 32px
}

#nav ul  { list-style-type: none; margin: 0; padding: 0; position: relative; width: 504px; height: 32px;overflow: hidden; }
#nav ul span  { display: none }
#nav ul li#bu1 a, li#bu2 a, li#bu3 a, li#bu4 a {position: absolute;width: 125px;height: 32px;bottom: 0;text-decoration: none;}

/* adjusted values for IE6 */
* html*li#bu1 a, * html*li#bu2 a, * html*li#bu3 a, * html*li#bu4 a { bottom: -1px; }

li#bu1 a  { background: url("media/botones/btn1_over.jpg") no-repeat; left: 0 }
li#bu2 a   { background: url("media/botones/btn2_over.jpg") no-repeat; left: 126px }
li#bu3 a   { background: url("media/botones/btn3_over.jpg") no-repeat; left: 252px }
li#bu4 a   { background: url("media/botones/btn4_over.jpg") no-repeat; left: 378px }

 li#bu1 a:hover,li#bu2 a:hover, li#bu3 a:hover, li#bu4 a:hover  { background-position: 0 -32px }