var cuantosbanners = 4; 
var ahora = new Date() 
var segundos = ahora.getSeconds() 
var banner = segundos % cuantosbanners; 
banner +=1; 

if (banner==1) { 
url=" http://www.e-buzones.com/ "; 
alt=" Visítanos ... "; 
imagen=" http://www.tucasaweb.com/banners/buzones1.gif "; 
width=" 468 "; 
height=" 60 "; 
} 
if (banner==2)  { 
url=" http://www.mallorcalandia.com/ "; 
alt=" Visítanos ... "; 
imagen=" http://www.tucasaweb.com/banners/mallorcalandia1.gif "; 
width=" 468 "; 
height=" 60 "; 
} 
if (banner==3) { 
url=" http://www.taxiface.com/ "; 
alt=" Visítanos ... "; 
imagen=" http://www.tucasaweb.com/banners/taxiface1.gif "; 
width=" 468 "; 
height=" 60 "; 
} 
if (banner==4) { 
url=" http://www.tecnorotul.com/ "; 
alt=" Visítanos ... "; 
imagen=" http://www.tucasaweb.com/banners/tecnorotul4.gif "; 
width=" 468 "; 
height=" 60 "; 
} 

document.write('<a href="' + url + '" target="_blank">'); 
document.write('<img src="' + imagen + '" width=' + width + ' height=' + height + ' alt="' + alt + '" border=0>'); 
document.write('</a>');