To set-up APC in magento, you need to install php_apc.dll to your extension directory, and then need to do setting to php.ini files, after then need define in local.xml file for APC calling.
Please follow below few links which will help you.
http://www.magentocommerce.com/boards/viewthread/8937/P0/ http://www.aitoc.com/en/blog/apc_speeds_up_Magento.html
http://magebase.com/magento-tutorials/speeding-up-magento-with-apc-or-memcached/ http://www.magecorner.com/magento-apc-cache/