var j, list = new Array();

var folder = "/images/home/right/";

list[list.length] = "rtpic01.jpg";
list[list.length] = "rtpic02.jpg";
list[list.length] = "rtpic03.jpg";
list[list.length] = "rtpic04.jpg";
list[list.length] = "rtpic05.jpg";
list[list.length] = "rtpic06.jpg";

j = parseInt(Math.random()*list.length);
j = (isNaN(j)) ? 0 : j;

document.write("<img src='" + folder + list[j] + "'>");