Drupal memcache and Apc Cache, how to make them both work?

Try this in your settings.php

$conf['cache_backends'][] = 'sites/all/modules/memcache/memcache.inc';
$conf['cache_default_class'] = 'MemCacheDrupal';
$conf['cache_class_cache_form'] = 'DrupalDatabaseCache';
$conf['memcache_key_prefix'] = 'SOME_PREFIX';

/**
* Add APC Caching.
*/
$conf['cache_backends'][] = 'sites/all/modules/apc/drupal_apc_cache.inc';
$conf['cache_class_cache'] = 'DrupalAPCCache';
$conf['cache_class_cache_bootstrap'] = 'DrupalAPCCache';
$conf['apc_show_debug'] = TRUE; // Remove the slashes to use debug mode.

You would proberly not want debug to be TRUE.