Tak for points =)
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "
http://www.w3.org/TR/html4/strict.dtd"><head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Untitled Document</title>
<style type="text/css">
div {
width: 600px;
height: 1000px;
margin: 0 auto;
background: yellow;
filter: alpha(opacity=40);
opacity: 0.4;
}
</style>
<script type="text/javascript">
window.onload = function(){
var o = document.getElementsByTagName("body")[0];
// Hvis der er tale om et element på siden,
// - bruger du linjen herunder i stedet:
// var o = document.getElementById("EtElementID");
var nW = document.documentElement.clientWidth;
var nSide = (nW-600)/2;
var nMaxLeft = nSide + (Math.random()*((nW-nSide)-(nSide+188))); // 188 = billedets bredde
var nMaxTop = Math.random()*(document.documentElement.clientHeight-65); // 65 = billedets højde
o.style.background = "url('
http://www.eksperten.dk/images/eksperten_logo.gif') no-repeat "+nMaxLeft+"px "+nMaxTop+"px";
};
</script>
</head>
<body>
<div> </div>
</body>
</html>