Howtoforge posted a tutorial about setting up Xen on CentOS 6.2

This tutorial provides step-by-step instructions on how to install Xen (version 4.1.2) on a CentOS 6.2 (x86_64) system. 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, but still use the same hardware.

  Virtualization With Xen On CentOS 6.2 (x86_64) (Paravirtualization & Hardware Virtualization)