$lifetimes = Mage::getConfig()->getStoresConfigByPath('checkout/cart/delete_quote_after');

or

$config = Mage::getStoreConfig('section_name/group/field'); //value
$config = Mage::getStoreConfig('section_name/group'); //array

http://stackoverflow.com/questions/4874171/get-config-data-to-javascript-file-magento

Save config: http://inchoo.net/ecommerce/magento/how-to-programmatically-change-magentos-core-config-data/
http://www.magentocommerce.com/wiki/5_-_modules_and_development/0_-_module_development_in_magento/how_to_add_a_custom_module_for_custom_admin_config_options

Magento access to config store

magento

PHP