I wouldn't really bother:
1. Xbox360 is VERY noisy to be of any use as a modern media appliance. It might have been cool ten years ago but these days you have several cheaper and QUIETER alternatives.
2. Xbox360 is DRM laden and locked down. You can play a DVD but that is pretty much it. Forget streaming video files from NAS/Network Shares unless you have a media streamer (i.e. PC) or formats that MS approves of.
Shame really as a modded classic xbox with XBMC beats the pants out of Xbox360. We're moving backwards instead of forwards.
Viable alternatives are mainly Atom and nVidia Ion GPU based hardware coming out onto the market.
I've recently acquired an Acer Revo. Its tiny, whisper quiet, comes with a Linux only option (read no $100 MS tax) and thanks to its Ion GPU can render 1080p h264 files whilst utilising 10% of the CPU (this is an Atom we are talking about).
All of this on XBMC on Linux. XBMC also offers a wealth of plugins that allow you to stream music, video from the net (you tube) etc.
Its sad state of affairs that it is the open source projects (i.e. non-funded and understaffed) that are leading the way in home entertainment usability whilst these multi billion multinationals are only concerned with limiting and controlling your experience, i.e. propriety formats, cables, DRM..... this shit never ends.