FUNZIONA...SOLUZIONE TROVATA!!! posto il codice per chiunque ha lo stesso problema:

<html>
<head>
<title>Documento senza titolo</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<script type="text/javascript">
var myRequest = null;
function createRequestObject() {
var ro;
var browser = navigator.appName;
if(browser == "Microsoft Internet Explorer"){
ro = new ActiveXObject("Microsoft.XMLHTTP");
}else{
ro = new XMLHttpRequest();
}
return ro;
}

var http = createRequestObject();

function handleResponse() {
if(http.readyState == 4){
var response = new String;
response = http.responseText;
var nomi = new Array();
nomi = response.split("|");
for (i=0;i<nomi.length;i++) {
var anOption = document.createElement("OPTION");
document.getElementById("foo").options.add(anOptio n);
anOption.innerText = nomi[i];
anOption.Value = i;
};
}
}

function sndReq(action) {
http.open('GET', 'ajax2.php?action='+action);
http.onreadystatechange = handleResponse;
http.send(null);
}
</script>
</head>

<body>

[foo]
<select name="foo" id="foo"></select>
<div id="ex4result"></div>
</body>
</html>


UN GRAZIE A fcaldera
ciao a tutti