"This tutorial provides step-by-step instructions on how to
install Xen (version 3.0.3) on a CentOS 5.0 system (i386).
"Xen lets you create guest operating systems (*nix operating
systems like Linux and FreeBSD), so called 'virtual machines' or
domUs, under a host operating system (dom0). Using Xen you can
separate your applications into different virtual machines that are
totally independent from each other (e.g. a virtual machine for a
mail server, a virtual machine for a high-traffic web site, another
virtual machine that serves your customers' web sites, a virtual
machine for DNS, etc.), but still use the same hardware..."