I run Boxee on two machines. First is a fairly modern Vista-running machine, connected via wired ethernet to my modem/router/switch/access-point. The second is a Dell Optiplex running XP that was being retired from university use when I got it, connected to the network with a Netgear USB WiFi dongle.
I have demonstrated that I can serously hinder the ability of the second to stream, simply by surfing the web via my netbook. I don't know which part of the chain is the weak point, and even the strong points are not strong on a PC that old. My friend Patrick says that running CAT6 through the home is kinda worthless for most people because home broadband bandwidth are and will be much smaller than even older WiFi protocols. I understand this and believe it, but problems like this make me wonder.