virtualbox.org

How can I run a guest Windows Server 2008 R2 with Hyper-V in a VirtualBox 4 VM on a 64-bit host? I want to create Hyper-V vms in the guest.
If this can be done, is there any special configurations that I should know about?

Can't be done.
Virtualizer inside of a virtualizer is not supported by VirtualBox.