Trying to change the label titles

I am trying to use template.php to rename one of the form labels, could someone please tell me why the following doesn't work? I have been searching for hours tonight on this, and cant seem to find any documentation on how to hook into contact correctly, please help!

function helpinghands_theme() {
  return array(
    'contact_site_form' => array(
      'arguments' => array('form' => NULL),
    ),           
  );
}

function helpinghands_contact_site_form(&$form)
{
	$form['mail']['#title'] = t('E-Mail');
}