Centering form doesn't work

Hey!
Great plugin, having just a little problem to center my form. I tried adding

/* for IE */
.newsletter {
text-align: center;
}

.newsletter table {
margin-left: auto;
margin-right: auto;
}

in the css and also centered about everything in the html but it just sticks to the left side.
Here the form html:

<script type="text/javascript">
//<![CDATA[
if (typeof newsletter_check !== "function") {
window.newsletter_check = function (f) {
    var re = /^([a-zA-Z0-9_\.\-\+])+\@(([a-zA-Z0-9\-]{1,})+\.)+([a-zA-Z0-9]{2,})+$/;
    if (!re.test(f.elements["ne"].value)) {
        alert("the email is not correct");
        return false;
    }
    if (f.elements["ny"] && !f.elements["ny"].checked) {
        alert("You must accept the privacy statement");
        return false;
    }
    return true;
}
}
//]]>
</script>
<div class="newsletter" align="center">
<form align="center" "method="post" action="http://www.maurduelichter.com/wp-content/plugins/newsletter/do/subscribe.php&quot; onsubmit="return newsletter_check(this)">
<table border="0" align="center" cellpadding="3" cellspacing="0" class="newsletter">
  
  <!-- email -->
  <tr align="center">
  <td align="center" valign="middle"><input name="ne" type="email" placeholder="your email adress" size="30" required>    <input class="newsletter-submit" type="submit" value="subscribe"/></td>
</tr>

</table>
</form>
</div>

Thanks for the help!

Cheers from Vienna
Daniel