form.html

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>

<form method="post" name="subscribeform" id="subscribeform" enctype="multipart/form-data">
    <table border=0>
        <tr>
            <td><div class="required">Email</div></td>
            <td class="attributeinput"><input type="text" name="email" value="" id="email" size="40"></td>
        </tr>
    </table>
    <input type=hidden name="htmlemail" value="1">
	<input type=hidden name="list[4]" value="signup">
	<input type=hidden name="list[2]" value="signup">
    <input type="hidden" name="subscribe" value="subscribe"/>
    <div style="display:none"><input type="text" name="VerificationCodeX" value="" size="20"></div>
    <button class='button' 
        onclick="if (checkform()) {submitForm();} return false;"
    >Subscribe</button>
    <div id="result" style="color: red;"></div>
</form>

<script type="text/javascript">
function checkform()
{
    re = /^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/;

    if (!(re.test(jQuery("#email").val()))) {
        jQuery("#result").empty().append("Please enter a valid email address");
        jQuery("#email").focus();
        return false;
    }

    if (jQuery("#password").val() == "") {
        jQuery("#result").empty().append("Please enter your password");
        jQuery("#password").focus();
        return false;
    }

    return true;
}

function submitForm() {
    successMessage = 'Thank you for your registration. Please check your email to confirm.';
    data = jQuery('#subscribeform').serialize();
    jQuery.ajax( {
        type: 'POST',
        data: data,
        url: 'http://newsletter.homologacao.devsys.nic.br/?p=asubscribe&id=3',
        dataType: 'html',
        success: function (data, status, request) {
            jQuery("#result").empty().append(data != '' ? data : successMessage);
            jQuery('#password').val('');
            jQuery('#email').val('');
        },
        error: function (request, status, error) { alert('Sorry, we were unable to process your subscription.'); }
    });
}

</script>