Tanmay,
P2P is perfectly legal. Besides, it cannot be made illegal due to it's distributed and anonymous nature. The centralized one (napster) was pulled down, as you know. Do you know that most linux distros and indie albums/videos are available on p2p? This is the cheapest and best distribution medium.The only thing at fault is the licensing and copywright framework,
afaik.
You can't, unfortunately, say which file is legal and hwich one is illegal by looking at the file name. most illegal releases are "released" by certain hacker groups and this fact will be advertised in the filename (reloaded, paradox). All the holl/bolly/etc movies and large s/ws are obviously illegal. As are keygens/cracks and sn files.