Before you tell Windows 7 the wireless security key, tick the Hide characters box and it cannot be seen. The landlord can also hide the SSID in the router's settings so no-one can "see" the network exists.
Contrary to popular myth, the Homegroup password is not the wireless security key. Windows 7 offers you that before it even knows there is a wireless network nearby. You don't have to use Homegroup - proper networking is also availablein W7.