Полный код:
<!DOCTYPE HTML>
<html><head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="/style.css" rel="stylesheet" type="text/css">
<script src="/lib/jquery.js"></script>
<script src="/lib/jquery.form.js"></script>
<script>
$(document).ready(function(){
$('#userF').ajaxForm({
success: function(html){
alert(html);
}
});
});
</script>
</head>
<body>
<form action="/uuu.php" method="get" id="userF" enctype="multipart/form-data">
<button type="submit">Найти</button>
</form>
</body>
</html>
uuu.php:
<?php
header('Content-Type: text/html; charset=utf-8');
echo '<li id="user"></li>';
?>