Does anyone know how hard it would be, or if it would be possible to write something that masquerades on the network as an airport express, coming up as an AirTunes output for other iTunes to connect to? I'm sure a lot of people have spare macs at home, old iBook 500's etc that sort of thing that could be put to use with something like this. I personally already have a wireless network and an old spare powerbook that this would be great for.
Edit: hmm i'm not the only one who's thought of this:
CocoaDev: AirTunes