I have used VirtualBox on a Windows machine for a one-box setup. 4.0.2 defaulted that the guest OS was connected by a virtual hub, and could see all packets passing to both the host and guest machine; this allowed ShowEQ to be installed on a guest OS, and everything just worked. Sometime between 4.0.2 and 4.0.8, that changed, now you need to edit the .vbox file and add a line stating
Code:
<ExtraDataItem name="VBoxInternal/Devices/e1000/0/LUN#0/Config/IfPolicyPromisc" value="allow-all"/>
with e100/0/LUN#0 changed to match which network card you want to make promiscuous; or you can use VBoxManage and change that policy via the command line.
Should work easily the other way, but with a few different network settings.