AQUI TIENES:
<!-- Esta debería ser tu página de inicio -->
<!-- Modificar únicamente las direcciones url -->
<html>
<head><script LANGUAGE="JavaScript">
function redireccionar() {
var url640x480 = "http://www.tu-sitio.com/640x480";
var url800x600 = "http://www.tu-sitio.com/800x600";
var url1024x768 = "http://www.tu-sitio.com/1024x768";
if ((screen.width == 640) && (screen.height == 480))
window.location.href= url640x480;
else if ((screen.width == 800) && (screen.height == 600))
window.location.href= url800x600;
else if ((screen.width == 1024) && (screen.height == 768))
window.location.href= url1024x768;
else window.location.href= url640x480;
}
</script>
<title></title>
</head>
<body onLoad="redireccionar()">
</body>
</html>
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