Ben Armstrong provides the community with yet another useful script.
Set vs = CreateObject("VirtualServer.Application")
Wscript.Echo "Available system capacity: " & vs.AvailableSystemCapacity
This will report the available system capacity as a percent. Note that this is specifically refering to the ability to reserve CPU resource for a virtual machine - and not how much CPU resource is actually being used. By default virtual machines have a CPU reserve of 0%. You could have any number of these virtual machines running - and still have this script report that 100% CPU reserves were available (as this is technically true). Though once you start setting CPU reserves on virtual machines - this script will tell you exactly how much CPU capacity you have left.
To read the original posting, or to comment and thank Ben Armstrong for sharing these scripts, go here.