I would have written this as a comment if my user status would allow me to. This is an addition to what james_fuller already explained:
You can connect to your VM to your host's NIC. It's like your host OS becomes a router for your VM. Thus your landlord's network won't see your VM at all but only your registered MacBook.
Read about Shared Networking in this KB entry:
You can enable Shared Networking in the preferences of your VM, a restart of the VM might be necessary.
Regarding your other question:
Do I provide them with the MAC address from the VM (windows 7) or from Mountain Lion?
MAC addresses are supposed to be unique and having two identical ones in one network would cause some trouble, as ethernet packets aren't transported to an IP, but to a MAC address. A switch for example wouldn't know where to send it's packets and bot MACs would receive only parts of the data.