images = new Array(2);

images[0] = "<a href = 'pages/24h/inscri.htm' target = 'I1'><img src='banners/banner1.gif' alt='24 Horas de Logística' style='border:0' ></a>";

images[1] = "<a href = 'pages/24h/inscri.htm' target = 'I1'><img src='banners/banner2.gif' alt='24 Horas de Logística' style='border:0' ></a>";

index = Math.floor(Math.random() * images.length);

document.write(images[index]);