Ok, see you didn't say you could just have him come over or you go over there and trade via hdd transfer or whatever. You wanted to do it over the internet, and that's just not possible with iTunes. There are p2p programs you could set up, or you could set up an ftp server. Things of that nature.
There's even an extension for Firefox called AllPeers that will allow you to straight transfer files. You could share your music folder to your friends, and they can browse and download your songs at leisure. If they share their music folder out as well, then you could do the same with their collection.
I was initially under the impression that you wanted a way for them to be able to listen to your music, not actually copy it from your system to theirs.
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