The extension is available from PECL [1].

There is another memcache PECL extension, but this one offloads the intricacies of communicating with memcache onto libmemcached and instead concentrates on exposing a sensible API and some cool features like asynchronous requests and read-through caching callbacks.

http://gravitonic.com/2009/01/new-memcached-extension



(1. http://pecl.php.net/package/memcached)