risolto cosi:
<!DOCTYPE HTML>
<html>
<head>
<title></title>
<script>
function Slow(objet1) {
var a = document.getElementById(objet1.id);
var b = document.getElementById(a.parentNode.id);
alert(b.parentNode.id);
}
</script>
</head>
<body>
<div id="colum1" class="colum">
<div id="1" class="widget">
[img]img/arrow-up.png[/img]
</div>
</div>
<div id="colum2" class="colum">
<div id="2" class="widget">
[img]img/arrow-up.png[/img]
</div>
</div>
</body>
</html>