Apple's video and audio streaming protocol, AirPlay, has had its private encryption key cracked which means in the future you might be able to get software, homebrew and open source alike, to do what requires proprietary or licensed devices like an Apple Airport Express or Apple TV to do today. James Laird is the one who reverse engineered the keys and has created an emulator called Shairport:

My girlfriend moved house, and her Airport Express no longer made it with her wireless access point. I figured it'd be easy to find an ApEx emulator - there are several open source apps out there to play to them. However, I was disappointed to find that Apple used a public-key crypto scheme, and there's a private key hiding inside the ApEx. So I took it apart (I still have scars from opening the glued case!), dumped the ROM, and reverse engineered the keys out of it. So, here is ShairPort, an open-source (Perl/C) replacement.

Finding a hardware box that's Wi-Fi enabled, has the appropriate audio or A/V output ports, and can be loaded with Shairport enabled software probably won't be easy, especially immediately, but the hacking community is nothing if not ingenious so it

[mafipulations via MacRumors]