codice:
<script type="text/JavaScript">
function copia(){
document.form1.foglia.value = document.form1.albero.value;
}
</script>

*************************

<body>
<form name="form1" method="post">
<input type="text" name="albero" value="">
<input type="text" name="foglia" value="">
<input type="button" value="copia" onClick="copia()">
</form>