I have been using and recommending Xen for Full Virtualization for a while now. Yet, when I tried to install Xen on my old PC that ran on AMD's Athlon XP processor, I was not able to enable Full Virtualization using Xen. I wanted to make my old PC a fully virtualized machine. So I evaluated a few virtualization applications to make that possible. That's how I ended up using VMWare.
This article explains how to enable virtualization using VMWare.