I saw this on the linksys web site:
http://www.linksys.com/servlet/Satel...=2202640536B05
I'm not sure if its the best way of doing it, but will definitely let you hook up your receiver to your computer via a wireless network. Also, it will appear as an actual sound card in your computer settings, so anything your computer can play will go through that.
If you want something that can actually pull the files across the network and play them, the squeezebox is the way to do it. The linksys thing is more of a "networked wireless soundcard" whereas the squeezebox is an actual media player that can read a network share.