You cannot stop P2P filesharing unless you completely re-engineer the internet, and make totalitarian internet-wide DRM the de facto standard.
You might not stop it, in the same way that you aren't ever going to stop shoplifting.
What you can do is educate people and make it less socially acceptable.

One of the main reasons people are stealing music at the moment is because they don't really consider it stealing.

Shoplifting is piss easy. As is dealing drugs. Both activities are illegal and there is always a chance of being caught and punished, however most people don't do it because of social pressures not to.

Make filesharing unpopular and frowned upon and you will have won half the battle.
More often than not its the social pressure not to do something rather than the potential penalties that dissuade people from acting.