iTunes 4 is great! I finally got iTunes to share music between the various computers in the house. First, all computers should be on the same network and the same subnet(1). When I told the desktop computer to use the DHCP connection provided by the Airport (via EtherNet), everything worked properly.
My roommate was also able to access my desktop's music library, as I was able to access his. It got interesting when he tried to play music that I had purchased from the Apple Music Store. I would have to "Authorize" his computer with my account information to allow this. Well, I already authorized the 3 computers Apple allows... my laptop, my desktop, and my server.
I can understand why Apple won't and should not allow you to copy music between computers but I would think if I just wanted to allow someone to listen to the music I purchased legally, *just listen to it*, I should be able to. In order to make the music I purchased available via iTunes I had to burn a CD, then re-rip it.
If people who are able to access your iTunes music library over the network are allowed to play the music you purchased from Apple, it will cut down on piracy.