<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"></script>
<script>
$(function() {
var o = $('.forname').on('change', "select", function() {
$('#adres').val($.map(o.find('option:selected'), function(i) {
return i.text
}).join(', '))
});
});
</script>
</head>
<body>
<form class="forname">
<select name="as[]">
<option>Text 1</option>
<option>Text 2</option>
</select>
<select name="as[]">
<option>Sub 1</option>
<option>Sub 2</option>
</select>
<input id="adres" />
</form>
</body>
</html>
Работает?