Make it easier, just get a cheap $20 router at walmart. It will handle the networking stuff for you and if you want the WDTV LIve to be wireless then it could then connect to that and stream from the laptop or whatever in the other room via the router of-course.
You don’t need an internet connection with a router. It will just fail to find an address but the DHCP will still hand out IP address to devices that are connected. Later on if you get internet, you already have a router so good to go!
Cheap switches are like 14.99 or something - i’ve seen cheap wireless router (Belkin) for $19.99 so not much more cost.
