How to run a XEN virtual machine ontop of a RHEL 7 installation and then run windows 7 pro 64-bit ontop of/in the XEN VM

I would like to run a XEN virtual machine ontop of an RHEL 7 installation and then run windows 7 pro 64-bit ontop of/in the XEN VM.

How best can I go about it.

Re: the baseline RHEL 7 is properly installed and ruing.