<script>
function LienAuHasard()
{
Url = new Array;
Url[0] = "http://www.site1.com";
Url[1] = "http://www.site2.be";
Url[2] = "http://www.site3.nu";
Url[3] = "http://www.site4.fr";

ChoixLien = Math.round(Math.random() * (Url.length+3));
window.open(Url[ChoixLien],'_self');
}

</script>

<script>location.href =LienAuHasard();</script>