Quick and dirty
<html>
<head>
<title>Test</title>
<script language="javascript" type="text/javascript">
rnd.today=new Date();
rnd.seed=rnd.today.getTime();
function rnd() {
rnd.seed = (rnd.seed*9301+49297) % 233280;
return rnd.seed/(233280.0);
};
function rand(number) {
return Math.ceil(rnd()*number);
};
function openMsg() {
var number = rand(5); //total number msg
if (number == 1) {
var msg = "Message 1";
}
else if (number == 2) {
var msg = "Message 2";
}
else if (number == 3) {
var msg = "Message 3";
}
else if (number == 4) {
var msg = "Message 4";
}
else if (number == 5) {
var msg = "Message 5";
}
document.getElementById('window').innerHTML = msg;
document.getElementById('window').style.display = 'block';
}
</script>
</head>
<body>
<a href="javascript:openMsg();">Click Here</a>
<div id="window" style="display:none; border:solid; height:200; width:400; left:100; top:100;"></div>
</body>
</html>