This article walks through the steps needed to install the libevent, memcached and PECL memcache libraries on Debian 4.0 (Etch). These are the prerequisites to being able to use the Drupal memcache module.
Read it at lillabot
Memcache consists of two parts; a server library which runs the caching daemon and a client library which allows PHP to interact with the server. The server library is called memcached and it depends on the libevent library, so the first step in the installation process is getting a recent copy of libevent.