I just thought of another "nice-to-have": I will need to be able to make this virtual machine start with Windows (preferably as a service without needing the user to login), and to have it shut down (paused is fine) when Windows shuts down.
I would guess all packages will offer this in some form or other, but vmware-server might just have the edge?
USB support may turn out to be necessary (it isn't yet, but it's a useful get-out-of-jail-free card to have on hand if I need it).