I bought a Roku Soundbridge recently to pipe my computer music to other areas of the house.
It has a wifi card or you can plug it into an ethernet port if you have your rooms wired. Next, you just run a program on your computer that accesses your music and it does the rest.

I wrote a review at the site below:

http://www.blog.uofmtiger.com/2007/09/03/oh-roku/

In the shot above, I am using a PSP as the remote control. You could also use a laptop or the remote that comes with the device.