Maybe this will help:
<html>
<head>
<script type="text/javascript">
function changeStyle()
{
var elem = document.getElementById("text");
elem.innerHtml= ""+""+""+"ABC";
document.body.Image="url(bgdesert.jpg)";
}
</script>
</head>
<body>
<div id="text"></div>
<input type="button" önclick="changeStyle()" value="Set background-image" />
</body>
</html>