There appears to be some work going on to try and get iPlayer working on the XBox Media Center according to this thread on their forums (thanks for the link, Iain) and although it only seems to make progress up to where I did, it does include this comment from Ian Forrester of backstage.bbc.co.uk (a terribly nice chap who I met at XTech 2007 in Paris, and who as it turns out used to DJ at a club I used to go to in Bristol)
We’re happy for people to hack around for non-commercial uses. which is really good to hear.
Additionally, tonight I came across WiidiaPlayer which is built in MTASC,
an open-source ActionScript 2.0 compiler written in OCaml and plays back RTMP streams. Wiidiaplayer is open source and that source is on Google Code. My initial tests haven’t been that successful, but they’ve only been ten minutes long 🙂