For Joomla 3.X
You need to override the cpanel component in your admin template by adding the file (and folder tree):
[tpl_xxx]/html/com_cpanel/cpanel/default.php
where tpl_xxx is your admin template to display by default.
Then you can display anything you like related to your component.
<?php
defined('_JEXEC') or die;
if(!defined('DS')) define('DS', DIRECTORY_SEPARATOR);
//Load pane behavior
jimport('joomla.html.pane');
jimport('joomla.application.component.model');
define(MYPATH_ADMINISTRATOR,JPATH_SITE.DS.'administrator'.DS.'components'.DS.'com_xxx'.DS);
require_once (MYPATH_ADMINISTRATOR.'models'.DS.'xxx.php');
JFactory::getLanguage()->load('com_xxx', JPATH_ADMINISTRATOR);
//initialise variables
$document = JFactory::getDocument();
$user = JFactory::getUser();
//load model
$xxxModel = JModelLegacy::getInstance( 'xxx', 'xxxModel' );
$extraData = $xxxModel->getExtraData();
//build toolbar
JToolBarHelper::title( JText::_( 'COM_XXX_XXX' ), 'home' );
...