//*******************************
// Put this in your template.php*
//*******************************

function _phptemplate_variables($hook, $vars = array()) {
// An anonymous user has a user id of zero.      
if ($user->uid > 0) {
	// The user is logged in.
	$vars['logged_in'] = TRUE;
}
else {
	// The user has logged out.
	$vars['logged_in'] = FALSE;
}
}

//*******************************
// Put this in your page.tpl.php*
//*******************************

<? if (($logged_in)){ 
   Do what to when logged in
}else
{
   do something else
}
 ?>