You could also run the cable through pipes outside, fit a junction box to
the outside wall of your house.
I'd use a switch in room A (they're very cheap and relatively power
efficient) and just have one cable from central hub. Allows for better
future expansion too.
If speed isn't an issue then you could look into using HomePlug adaptors -
works fine for my parent's iPlayer on Freesat box.
http://en.wikipedia.org/wiki/HomePlug (they can be quite fast in the right
circumstances, but I'd definitely opt for cat5e in my bandwidth hungry and
latency sensitive household).
Cheers,
Benjie.
