Do you want to SHARE the music or COPY the files to another machine? You're asking two different questions.
iTunes will let you share your library over a home network where the other users can only listen to it, and not actually grab the files. Not a problem if the computer sharing it is always on.
If you want to copy the files to another computer, assuming you're talking about iTunes DRM protected songs, you can authorize several (5?) other devices to play those songs. If the songs aren't DRM protected, you can copy them like any other file using file sharing.