Although Hamachi for OS X is still terminal based, try the unofficial HamachiX with a gui front end. (HamachiX works for me with friends using hamachi on XP.)
- Install Hamachi and create a new network. A simple name and password.
- Enable sharing in iTunes
- Have your friend install Hamachi and log on to the network you created.
- You will have to restart you iTunes on your pc after they join your 'network'.
- Just like on a regular network, both ends need to have iTunes 'open'.
- Share your music.
- Linux users use banshee with the 'daap' plugin to share with iTunes.
- To download your friend's (or whatever) library use ourTunes.