while(true){
aleatorio = Math.random();
numero = Math.round(aleatorio * 1);

if (numero == 0){
imagen = "http://img94.imageshack.us/img94/8489/pmabanner.png";
break;}

if (numero == 1){
imagen = "http://img94.imageshack.us/img94/8489/pmabanner.png";
break;}

}
document.write('<a href="http://pmaclan.forumdomtom.com/" target="_self" ><img src="' + imagen + '" border=0 style="width: 280px; height: 88px"></a>');