while(true){
aleatorio = Math.random();
numero = Math.round(aleatorio * 10);

if (numero == 0){
imagen = "http://img21.imageshack.us/img21/2808/logo1msj.jpg";
break;}

if (numero == 1){
imagen = "http://img33.imageshack.us/img33/5809/logo4vcr.jpg";
break;}

if (numero == 2){
imagen = "http://img33.imageshack.us/img33/1057/logo5y.jpg";
break;}

if (numero == 3){
imagen = "http://img300.imageshack.us/img300/9731/logo2v.jpg";
break;}

if (numero == 4){
imagen = "http://img252.imageshack.us/img252/8172/logo3r.jpg";
break;}

}
document.write('<a href="http://pokemonroldream.foroactivo.com" target="_self" ><img src="' + imagen + '" border=0 style="width: 700px; height: 200px"></a>');