Need advice on how to network iTunes libraries

I have four computers sharing a wifi network at home. Three of the computers are Windows based and one is a Mac pro running SL 10.6.3. All machines have the latest version of iTunes on them. Each computer has its own iTunes library. What I would like to do is have one central network hard drive that all the computers can use as a library. If I add a song or playlist on one machine I want it to show up on all the machines. I realize that I can probably only have one instance of iTunes running at a time for it to work but I don't want to have to add new music to each machine manually.

My ultimate goal is to have all the computers sharing one common library and set of playlists, and to minimize any chance of having duplicates on any of the machines.

Does it matter that the network drive is formatted for Windows or Mac?

What is the simplest way to accomplish these things?

You can accomplish this through home sharing. You designate one of your computers to be the main library and set it up with iTunes and all your media. Set up home sharing on all your computers (all you have to do is choose the home sharing menu option and enter your iTunes credentials). Then all your other computers will have a listing in iTunes for the library on the "main" computer. It will be on the left side above where the playlists would be.

Add new media to the main computer and you can stream it to all the others this way.

Note that this is streaming only and does not create a replica library on each computer. I don't believe that is possible.