<form onsubmit="return false;" action="deine_seite.php" method="post" id="deine_form_id">
<!--
Deine Input-Felder usw.
-->

<input type="submit" name="save" id="save" />
</form>

<script type="text/javascript" language="javascript">

$('save').observe('click', saveData);

    function saveData(event) {
        new Ajax.Request('deine_seite.php',
        {
            method: 'get',
            parameters: $('deine_form_id').serialize(),
            onSuccess: handleResponse
        });
    }

    function handleResponse(response) {
        if (!response.responseText.isJSON()) {
            $('updateErrors').innerHTML = "";
            $('updateErrors').innerHTML = "<p class='success'>"+response.responseText+"</p>";
            $('updateErrors').style.display = "block";
            return;
        }

        var data = response.responseText.evalJSON();

        var error = "<p class='error'>";

        if (typeof(data) == 'object') {
            for (var item in data) {
                error += data[item] + "<br />";
            }
        } else {
            for (var i = 0; i < data.length; i++) {
                error += data[i] + "<br />";
            }
        }
        error += "</p>";
        $('updateErrors').innerHTML = error;
        $('updateErrors').style.display = "block";
    }
</script>