QUOTE(Vidness @ Jun 28 2007, 11:28 AM)

Can a 'game' be an application that can open .avi .mkv, .ogm, and .mp4 files across a samba-shared network?

Well, first off, I haven't been able to find any support of video formats in XNA. The decoders could be written in C#, but I'm sure they'd take a performance hit at that high of a level.
Second, there is no network support (yet). I think Microsoft is waiting to see if anybody can break their XNA C# "sandbox" before opening up network capability. Even if they do open it up - it will be to access Live and maybe media files via their Zune gateway.
Don't let this put you off, though. XNA is pretty powerful, but it's meant as a legitimate outlet for homebrew game designers. I'm pretty sure that the guys behind XNA were very familiar with the homebrew scene - I suspect their "Marblets" may be an homage to my own "X-Marbles" homebrew for the Xbox (I consider it to be the first "complete" game in the homebrew scene - gameplay, sound, music, high score, though a Pong clone preceded it by a week or two). It's just not set up to code XBMC; I think Microsoft intends to leverage the dashboard for that, as it ties into th marketplace strategy, and Microsoft is, after all, out to make a buck or two on the 360.