One thing I find interesting is that many people tend to overcomplicate things when trying to achieve nice things like shared music from a central location. Usually people achieve this by using Rendezvous for doing a multicast DNS server, and then using something like daapd to stream the files wirelessly over a network. While there is nothing wrong with this, and indeed, be my guest if this method suits you better,
However, there's a very simple way of doing this: make a file server! It doesn't matter what operating system the server is running, so long as it can serve files in a protocol your computer can understand. I recommend using the SMB protocol, as it's the easiest and most universal (and if you're using Windows, you'll pretty much have to). Another good choice is NFS if you're running mainly *nix-based systems.
Now, for connecting. On Windows systems it should be present under Network Neighborhood, or you can just type the server's IP address/hostname into the address bar: \\192.168.0.1. On Mac OS X, hit Apple-K in the Finder to bring up the connection window, and enter your server's IP address/hostname: smb://192.168.0.1. It should then prompt you for a username/password, after which it will mount the volume onto your desktop. Or you can do it from the terminal on any other type of Unix system:
mount -t cifs //192.168.0.1/share /mnt/point
...for example.
Copy your entire iTunes folder onto the file server. Everything: configuration files, library files, everything.
Finally, In iTunes, under Preferences/settings, go to the "Advanced" tab. For "iTunes Music folder location", go to the location of the network folder that you copied the iTunes folder to, and choose "iTunes Music". Hit "okay", and voila! You now have a shared library. This has some advantages to a streaming iTunes server, most notably a shared library. This way, your library can still keep track of play count, ratings, you can easily tag songs, and add to and remove from your collection. The only thing an iTunes server would have let you do would be stream the content!