put data into a table with ajax

[ragtek]

some of the output in VB are ajax-based, eg. the ignore/buddy list

how exactly does that work?
i have a small form that is located in a pop up menu.
here i write my category name and click save
now the thing should be stored into the db and put into a table wich shows all my categories
that works at moment fine with new loading
but i'd like to make it with ajax=> no reload

can somebody help me?

this is at moment my code

if ($_REQUEST['do'] == 'dokat')
{
$vbulletin->input->clean_array_gpc('p', array(
'katname' => TYPE_STR
));

$a = $vbulletin->GPC['katname'];
$db->query_write("
INSERT INTO " . TABLE_PREFIX . "musikkategorie
(userid,bezeichnung)
values
(" . $vbulletin->userinfo['userid'] . ", '" . $db->escape_string($vbulletin->GPC['katname'])."')");

// now normaly the reload but here now xml part
require_once(DIR . '/includes/class_xml.php');
$xml = new vB_AJAX_XML_Builder($vbulletin, 'text/xml');
$xml->add_group('katliste');

$xml->add_tag('katname', $a);

$xml->close_group();
$xml->print_xml();

}

now i need a java script witch shows the katname?