One low cost solution is the Slim Devices Slimserver and Squeezebox music players. The Slimserver software is FREE, just download and install. It includes a software emulator of a Squeezebox music player (softsqueeze) that you can run on PCs on your home network and it is also FREE.
If you decide you would like a hardware music player (Squeezebox2) to hook to your stereo they start at $199 for the hardwired version and a version with built-in 802.11g wireless is $279.
I prefer this over dedicated whole-house solutions like A-bus for the following reasons:
-Unlike the keypads to whole-house systems that just show you volume level and which soource you have selected, a squeezebox2 has a bright display that shows you artist and track info, current song playing via internet radio, etc.
-Controlled from infrared remote so it works with universl remotes and Home Automation controllers with IR capabilities.
-Can also be controlled by built-in browser interface or though a Home Automation controller by means if xPL/xAP or Command Line API.
-All players (hardware or free softsqueeze instances) can play in sync or independently.
-You can start with $0 investment (using only software players and existing PCs) and add hardware players whenever you want. (I think the server can handle 20+ separate streams on fairly modest server hardware).
-You can send home automation messages to the music player displays.
-When hardware players are off they can display the time, do a headline ticker from RSS feeds (like Cocoontech) or other display options.
-Will play most any file format out there.
Etc. etc. etc.... Check it out at
http://slimdevices.com/