LinuxMCE differs from other Home Theater PC systems in that some functions are performed by a Core PC and some functions are performed by a Media Director PC. A hybrid Core/Media Director PC does both.
For the central LinuxMCE Core server that will function on a home automation network, most recommended installations suggest 2 network interface cards (NICs). If you don't have a second NIC card already installed, it is easiest to do so before installing Kubuntu/LinuxMCE, since the second card will then be recognised and configured correctly during the initial installation. You won't have to fiddle with setting it up later. See this section for tips on setting up a nested LinuxMCE LAN within an existing home LAN.
(If you will have only a single PC acting as a hybrid Core/Media Director, 2 cards aren't strictly necessary, but putting them in at this stage will allow you to expand your network down the line.)
For a PC acting as a Media Director (either as a standalone or as a hybrid), an nVidia graphics card is strongly recommended so that you can display the User Interface in the highest resolution (UI2). If you don't have one installed, it is easiest to do so before starting software installation. It is probably best to stick with an nVidia card on the Core PC as well. Make sure the card is installed prior to software installation.
Check out this video and example installation of a complete installation that took this guy a few days and will likely take you a few weeks.