Windows: good, simple music streaming?
Solution 1:
Have a look at the newly-released from beta Audiogalaxy...featured by Lifehacker.com, it has clients for Mac OSX and Windows...iPod/iPhone, and Android apps also exist.
Highly recommend, works well, and fast!
Solution 2:
You may want to give VLC a try. I've only ever used it as a player (which it's great at), but it was initially designed to be a media streaming server. It sounds like it should fit your needs pretty well. Plus, it's cross-platform! VLC can stream from a video file on the hard disk, a DVD or CD, a digital TV card, or other video input devices.
Solution 3:
Linux + MPD
Can't really beat that combination IMHO.