First go to the place in the house where all the wires come together. That's where your switching center will be. That's also where your cable modem or DSL modem should be. Next, install a broadband router. Typically, broadband routers come with only 4 ethernet ports for connecting clients. You mentioned at least 4 possible client systems/devices, and based on your excitement, surely you have more than 4 ethernet jacks all around your new house. Thus you will need to install an additional plain switch beside the router. Switches typically come in 5-port and 8-port configurations, which would give you a total of 7 or 10 available connections, respectively.

If you need more than 10, just get two switches. If you use more than one additional switch, you should configure them so that each receives a direct uplink from one of the ports on the router. Technically you can daisy-chain them from router to switch1 to switch2 to switch3, etc, but from a practical standpoint you start having little problems in the third layer. Therefore, have one uplink from the port1 on the router to switch1, a separate uplink from the router port2 to switch2 and yet another separate uplink from the router port3 to switch3. Then connect all your household network runs to the switches. I recommend you put in enough switch capacity to cover 3-5 more ports than you have network runs. That way every jack in the house will be live, even if you aren't using the jack in that room right now, plus you will have a few spare places to plug in something extra in the future.

Now you have a fully functional network, all controlled from that central location. Set up your computers and plug network cables from the computers to the jacks in the wall and they should be connected. Note that you will need to configure the broadband router for the specifics of your cable or DSL system, but once that is taken care of, any computer on any jack in any room in the house should be able to get an internet connection. You'll need to check with your office IT department about configuring the VPNs.

Finally, a word about wireless. You've got lots of wired connectivity, but sometimes wireless is nice too. Using a laptop away from the network jack (the garden? the bathroom?) is possible with wireless. You mentioned iTunes - the Apple Airport Express is a neat little wireless receiver that can take the music being played by iTunes and pipe it into an audio input of your home stereo system. If any of these ideas capture your imagination, you need to install a broadband router (which we talked about up there in the first paragraph) that has an integral wireless access point. But remember to secure it properly!!!!

Now, the one thing I didn't say anything about is the Media Center PC and the plasma TV. I don't have much experience with any of that, so somebody else will have to cover that area.

dw