Right. All you need is a NAS device which supports UPnP, and runs some sort of server software, like twonky(?) - some will now do this out of the box, rather than you having to install it yourself. There is a useful article
here which should get you going, and has reviews of some devices, UPnP and not. The soundbridge
is UPnP compatible, I checked, and so will talk to a UPnP server.
I only warn against the MyBook (NAS edition) because reviews tell of it having appalling access speeds, which would drive me mental.
Another option is AppleTV, which either streams music and video while your computer is on, or stores it on its own hard drive for when it's not. Fabulous interface, but needs a telly to navigate, which may not be where you want your music to be.
Don't worry baby I'm safe and sound.
My useful posts: