function cambiarImg(imagen)
{
	var divImg = document.getElementById("headerbck");
	divImg.style.backgroundImage = "url(images/bg_top" + imagen +".jpg)"; 
}
	
	
function getBrowserHeight() {
          var intH = 0;
          var intW = 0;

          if(typeof window.innerWidth  == 'number') {
             intH = window.innerHeight;
             intW = window.innerWidth;
          } 
          else if(document.documentElement && (document.documentElement.clientWidth || document.documentElement.clientHeight)) {
               intH = document.documentElement.clientHeight;
               intW = document.documentElement.clientWidth;
          }
          else if(document.body && (document.body.clientWidth || document.body.clientHeight)) {
            intH = document.body.clientHeight;
            intW = document.body.clientWidth;
          }

          return {width: parseInt(intW), height: parseInt(intH)};
      }


      function SetLayerPosition(idDiv) {
          var elem = document.getElementById(idDiv);    
          var bws = getBrowserHeight();
 
          elem.style.left = parseInt((bws.width -  elem.style.width)/2);
          elem.style.top =  parseInt((bws.height - elem.style.height)/2);
         
          elem = null;
      }

      // window.onresize = SetLayerPosition;
      // window.setInterval('SeyLayerPosition();', 100)