So What's XCache ? XCache is a powerfull PHP Accelerator (similar to APC, eAccelerator, etc). It's stable enough and really very fast.
Important: This tutorial assumes that you already have a running webserver (Apache) and PHP installed.
Let's install XCache. First of all I recommand doing a full upgrade of your system, for that do :
# apt-get update && apt-get dist-upgrade
Once that's done all we need to do is :
# apt-get install php5-xcache