в аякс пшп

добавить

'p_preview' => array('user'),

function p_preview()
{
global $template, $board_config, $lang;

$text = get_param('text', '');
$subject = get_param('subj', '');

$template->set_filenames(array(
'preview' => 'posting.tpl')
);

$msg_data = _p_preview($text, $subject);
$template->assign_vars(array(
'TOPIC_TITLE' => $msg_data['subject'],
'POST_SUBJECT' => $msg_data['subject'],
'POSTER_NAME' => $preview_username,
'POST_DATE' => create_date($board_config['default_dateformat'], time(), $board_config['board_timezone']),
'MESSAGE' => stripslashes($msg_data['message']),

'L_POST_SUBJECT' => $lang['Post_subject'],
'L_PREVIEW' => $lang['Preview'],
'L_POSTED' => $lang['Posted'],
'L_POST' => $lang['Post'])
);

$template->pparse('preview');
}
в тпл
<input type="button" id="preview" class="mainoption" value="предпросмотр" />

<script type="text/javascript">{
post_text = msg.html();

msg[0].innerHTML = '';
msg.html(cont);

$('.ajax_qei').hide();
msg.find('#send').click( function() {
ajax_query(function(cont) {
postedit_mode = false;
if(ajax_error(cont)) return;
msg.html(cont.substr(1));
$('.ajax_qei').show();
}, {mode: 'p_send', p: pid, text: msg.find('#message').val()});
});

msg.find('#preview').click( function() {
ajax_query(function(cont) {
if(ajax_error(cont)) return;
msg.find('#preview_inline_box').html(cont);
}, { mode: 'p_preview', p: pid, text: msg.find('#message').val() });
});

msg.find('#cancel').click( function() {
postedit_mode = false;
msg.html(post_text);
$('.ajax_qei').show();
});
</script>