<script language="javascript">
var MAX_INDEX=4;
function change(ddd)
{
if(ddd.style.zIndex<= MAX_INDEX)
{
ddd.style.zIndex = MAX_INDEX+1;
MAX_INDEX++;
}
}
</script>
<div id="layer1" onclick="javascript:change(this);" style="position:absolute;margin-left:100;margin-top:50px;margin-=100;width=100;height=100;background-color:#ff0000;z-index:1"></div>
<div id="layer2" onclick="javascript:change(this);" style="position:absolute;margin-left:120;margin-top:60px;margin-=120;width=100;height=100;background-color:#00ff00;z-index:2"></div>
<div id="layer3" onclick="javascript:change(this);" style="position:absolute;margin-left:140;margin-top:70px;margin-=140;width=100;height=100;background-color:#0000ff;z-index:3"></div>
<div id="layer4" onclick="javascript:change(this);" style="position:absolute;margin-left:160;margin-top:80px;margin-=160;width=100;height=100;background-color:#000000;z-index:4"></div>