I remember that meeting. Being a Linux Users Group, I think the meeting focus was more on "running Linux on your XBOX", but touched on XBMC as another thing you can run.  I ran it at home in NZ, it's fantastic: open source, and being ported to Linux for use on other hardware. (Compiled versions for the XBOX are of dubious legality due to Microsoft only allowing partners to compile using the SDK, and then only for "boxed product".

Installing XBMC for XBOX comes down to "mod your X-Box and then put a CD in."  You could run through that as a meeting demo if you wanted to prove how easy it is! The tricky part is finding the CD, as it is usually acquired from a friend, IRC channel or BitTorrent, due to the aforementioned SDK issues.  Information on how to do this is a quick Google search away.

Craig