Was thinking about this the other day. You pretty much want simplicity. XMBC makes a "live" distribution. Meaning its basically XBMC already setup on linux, runs straight off a DVD and can be installed.
http://xbmc.org/download/
If you already have the hardware you are going to run this on, just download the "live" iso from the xbmc site, burn it to DVD, then pop it in your computer and boot from it.
Some XBMC interface pics. Yes, it does look like this on your HDTV.