Posting Preview Example

Hi,

I was searching some example for how to preview a posting, how it will be look like, which has some images also, before submit. If i could pass the form_state parameter into my hook_theme function, then it was possible. But i don't know, how could i pass it there. I don't know any alternative about that.
Its just like the forum posting here. Could any one give me some hints about that ???

My Code like this:

function postings_add()
{
    return drupal_get_form('my_postings');
}


function my_postings($form_status)
{
    ....
    ......
    return $form;
}

function postings_theme() 
{
  return array(
    'my_postings_add' => array(
      'arguments' => array('content'),
    );
}

function theme_my_postings_add($form)
{
    ......
    $output .= drupal_render($form);
    return $output;
}