So you still want to use P2P, but legally...
Aside from copyright considerations, there are security aspects you might want to consider before opening up your computer for file sharing.
Peer-to-peer (P2P) file sharing applications such as BitTorrent, Kazaa, Ares, and Gnutella can render the private contents of your computer - your confidential data files, saved emails, financial records, etc. - vulnerable to exploitation. For this reason, ISPRO strongly recommends against installing and using these applications. If you have a peer-to-peer file sharing program already installed, we recommend you remove it. At the very least, disable your peer-to-peer software's uploading capability. To find out how, visit Cornell University's How to Remove P2P Applications web page.
OS File Sharing (Windows, Mac, Linux)
Unless it's absolutely essential that other people be able to access non-copyrighted materials on your computer, we urge you to disable the general file sharing capabilities of your operating system. Computers that have file sharing turned on are tempting targets for hackers, who often exploit that feature to take over victims' machines. Need help disabling file sharing on your computer? Check out the online Help features of your system or visit the web site of the operating system vendor (Microsoft, Apple, etc.) for more information.
Of course, just as you should avoid sharing your computer with everyone on the Internet, you should also prevent anyone else from using your machine or your computing accounts directly. Use a strong password, keep the password a closely-guarded secret, and turn off your computer when you're not using it. To find out more about creating a strong password, visit http://its.virginia.edu/accounts/passwords.html
Shut the door on hackers and other computer vandals. Don't share your files.