function addEvent(obj, evType, fn, useCapture){
		if (obj.addEventListener){
			obj.addEventListener(evType, fn, useCapture);
			return true;
		} 
		else if (obj.attachEvent){
			var r = obj.attachEvent("on"+evType, fn);
			return r;
		} 
		else {
			return false;
		}
}

var ancho = 200;
var alto = 300;
var interval;

function init(){
	var el = document.getElementById('banner_mov');
	var anchotot = (770-ancho)/2;
	var altotot = ((screen.availHeight-alto)/2)-60;

	el.style.display = 'block';
	el.style.left = anchotot+'px';
	el.style.top = '-'+alto+'px';

	mover('banner_mov', altotot, 5, 1);
}

function elimina(){
	mover('banner_mov', '-'+alto, 7, 0);	
}

function mover(id,y,velocidad,elimina){ 
	clearInterval(interval);
	var elemento = document.getElementById(id); 
   var hs=(elemento.offsetTop <y)?1:-1 ;
   hI=Math.ceil(Math.abs(y-elemento.offsetTop )/(11-velocidad)) ;
   elemento.style.top  = elemento.offsetTop +(hs*hI) + "px" ;
   if(elemento.offsetTop < y && hs==1){ 
     interval = setInterval("mover(\""+ id +"\","+ y +","+ velocidad +","+elimina+")",50);
   }else if(elemento.offsetTop > y && hs==-1){
	  interval = setInterval("mover(\""+ id +"\","+ y +","+ velocidad +","+elimina+")",50);
	}else if(elimina == 0){
		elemento.style.display = 'none';
	}else if(elimina == 1){
		setTimeout("elimina()",10000);
	}
}

if (document.getElementsByTagName) addEvent(window, 'load', init, false);