Ändra text med javascript

Modifierat ett script från Jojoxx.net.. ( http://www.jojoxx.net/css/dhtml/desclink.html )

<span id="desc" style="position: absolute;">Hejsan</span><br>
<script language="Javascript" type="text/javascript">
<!--
var Id = "desc";
function describe(string){
if(document.layers){
with (document[Id].document){
open();
write(string);
close();
}
} else if (document.all){
document.all[Id].innerHTML = string;
} else if (document.getElementById){
jxdocrange = document.createRange();
jxdocrange.setStartBefore(document.getElementById(Id));
while (document.getElementById(Id).hasChildNodes()){
document.getElementById(Id).removeChild(document.getElementById(Id).lastChild);
document.getElementById(Id).appendChild(jxdocrange.createContextualFragment(string));
}
}
}
//-->
</script>
<br>
<a href="javascript:describe('Svejsan')"><img src="bild.jpg"></a>