Free shipping only for registered users

$defaultGroup = Mage::getStoreConfig('customer/create_account/default_group');
$session = Mage::getSingleton('customer/session');
 
$allowedGroups = array();
if ($this->getConfigData('group_ids')) {
	$allowedGroups = explode(',',$this->getConfigData('group_ids'));
}
 
if (in_array($defaultGroup,$allowedGroups)) {
	$checkIfSignedUp = true;
}
 
if (count($allowedGroups) > 0) {
	if (!in_array($session->getCustomerGroupId(),$allowedGroups) &&
		(!$checkIfSignedUp || ($checkIfSignedUp === true && !$session->getIsSignedUp()))
	) {
		return false;
	}
}

$session = Mage::getSingleton('customer/session');
if (!$session->isLoggedIn() && $method == 'register') {
	$session->setData('is_signed_up',true);
} else {
	$session->setData('is_signed_up',false);
}

<?xml version="1.0"?>
 
<config>
	<sections>
        	<carriers>
			<groups>
				<freeshipping>
					<fields>
						<group_ids translate="label">
							<label>Customer group ID-s</label>
							<frontend_type>text</frontend_type>
							<sort_order>3</sort_order>
							<show_in_default>1</show_in_default>
							<show_in_website>1</show_in_website>
							<show_in_store>0</show_in_store>
							<comment>ID's of customer groups that qualify for free shipping (ex 1,4,7). Leave blank for all.</comment>
						</group_ids>
					</fields>
				</freeshipping>
			</groups>
		</carriers>
	</sections>
</config>