This can be done using custom properties very easily. Using the 'Custom Property Editor' located on the main Orion server create a new property under the 'Nodes' table named something like 'Physical/Virtual' or similar and then enter either 'Physical' or 'Virtual' for each row or device.
Once this has been completed return to the main Summary page and amend the 2nd level grouping to be the name of your new custom property!
This means that under 'Windows' you will now have 'Physical' or 'Virtual'
Hope this helps
You could create two node lists and have one with only Virtual one using this filter:
"nodeid in (select nodeid from VirtualMachines)"
and another that is not from that list
"not nodeid in (select nodeid from VirtualMachines)"