The Airport express is. Its works fine with a PC. Do you use iTunes? The Express was meant to be a small portable wireless station for on the road use. Such as when at a hotel with an ethernet port for internet. Plug the Express in and you now have wireless in your room. The audio thing was just an added bonus. It also has a USB port for a printer.
Here is the product:
http://store.apple.com/us/product/MB321LL/A/AirPort-Express-AirTunes?mco=MTY3ODQ5OTY
I looked around on Newegg.com and there are a few things out there that do similar things. Some cost a lot and some would not be very portable. And most do much more than music - probably means they are a pain to setup.