Ok, so back in December Rogue Amoeba announced they were coming out with a new app called
Slipstream that would let you stream audio to the AirPort
Express from any program (not just iTunes). Well, just over two months later they've finally released the app, only now
it's called Airfoil. Only compatible with Macs for the moment, but they admit that sooner or later they'll have to port
this to Windows.