Welcome Karl!
System requirements are hard to determine.. it depends on what you're doing,.
Linuxmce is a mesh of a bunch of programs, Pluto (
www.plutohome.com), Asterisk, MythTV etc.
First, you need to determine what you want it to do:
Obviously, you need some form of tuner or capture card if you want to record TV..
you can have multiple cards as well, but then, the requirements go up.
in a nutshell, linuxmce requires a Backend computer. This computer may or may not have a front end on it.
(a dedicated backend sits in the closet and grinds away)
Front ends are PC's (or other hardware) that interface to the back end.
They are called Media Directors, and you can have as many of those as you need.
Then there are the Orbiters, (fancy name for remote control). Normally, all Media directors have orbiters built into them.. but you can also have a Pocket PC as an orbiter.. etc.
Video cards are the tricky part... Newer Nvidia seems to work best..
so, to start out with, get your biggest machine, and set that up as the back end server....
then go to a smaller machine and set it up as a media director... etc...
BTW, the media directors (if properly configured) can PXE boot off the server, so you can have diskless MD's
HTH
Dan