Are you thinking of having just one computer in the living room or do your think of having a server somewhere with all the drives and running a diskless MD in the livinroom?
If you are going for a single PC install with all the drives on that, you can use wireless for internet. No problem. If you are going this route, LinuxMCE might not be the best software for you... If all you need is the media part (Movies, Music, Pictures and MythTV) then you really should look at MythBuntu... They have a livecd you can boot and try http://www.mythbuntu.org
If you are going for a 2+ pc install with one Core/Hybrid (Your server) and one or more diskless MD's then wifi is not usable. To run diskless MD's a cable is the only way. Wifi does not support PXE boot.