You can use the Joomla API to easily redirect to another url and display a relevant message after the redirection.
Joomla 1.5
global $mainframe;
$link = 'http://www.minitek.gr/';
$msg = 'You have been redirected to Minitek.gr';
$mainframe->redirect($link, $msg, $msgType='message');
Joomla 2.5
$app = JFactory::getApplication();
$link = 'http://www.minitek.gr/';
$msg = 'You have been redirected to Minitek.gr';
$app->redirect($link, $msg, $msgType='message');
where
$msgType can be
message,
notice or
error.