Remember these few points with PTP file-sharing:
You cannot share files that you do not own, unless given express consent by the owner to do so (and make sure to get this in writing).
If you own the work of art like a music file and want to share it with the world, you can freely do so.
Works of art like music files do not have to be registered with the Copyright Office to be protected by copyright law. A work of art, such as a music piece, is automatically copyrighted the moment it is put into some type of medium (e.g. CD, DVD, tape, or any other file that is on your computer). However, copyrighting works of art, like music, with the Copyright Office does give the owner more legal protections.
Finally, take a look at
"Is Limewire Legal?" for further details on the legalities of peer-to-peer file sharing.