This install procedure can be used in a generic OpenVZ or Virtuozzo environment or inside an all in one OpenVZ installer+GUI product such as Proxmox VE.  I am not sure how relevant it would be for Xen.  This guide covers the installation INSIDE an already created OpenVZ/Virtuozzo container (VPS sans Operating System) which would then become a functioning Virtual Private Server (VPS).  I will not be covering the OpenVZ host setup or iptables or zaptel/dahdi setup inside or outside the OpenVZ environment.