Re Craigs answer. The IIC with the proper driver can go a mile (see Philips appnote), the maximum length for 485 is 4km - transmission speed dependent, the maximum number of nodes is specified as 32 LOADS and quarter load chips are available i.e. 128 nodes is possible. I have heard rumors about chips with even lower loads. I would, if I were to design such a system, use the RS-485 approach.
Do'nt get tangled up in the wires,
Erik