you can always use Vmware 3.5 ESXi 
Yes, ESX has a certain appeal being bare metal. The appeal of Xen is the ability to pass specific hardware (say special PCI cards) straight through to the guest OS. To my knowledge, ESX can't do that.
I'm looking around for a simple Xen install solution as well. Then I will have to find a clever way of moving my beast of an SME (almost a tera of disk space) onto it hopefully without having to go buy new hard drives.
For now though, I'm running VMWare 2 on SME.