each box needs a cat5, if theyre connected to a hub switch, this then needs to be connected to a router as well, so you could have main box downstairs with card in connected by cat5 to router, then 2 upstairs both with own cat5 to a hub, then a single one from this to the router
in my house, i have 3 boxes upstairs, an xbox360 and a computer all connected to an 8 way hub, this then has a single cat5 to a router in the cupboard, in the living room i have another 360, laptop, dreambox, tm6800super and tm500, all connected to a hub, then a single cable to the router, the kitchen has another hub with a PC and 2 more receivers, again a single cable to the router
then in the cupboard with the router is another receiver acting as my server, connected directly to the router
the router deals with all the addressing issues m8, except for the server, which always has the same IP address for the other boxes to look at