I've always been curious about D2 PvP, is it like a world PvP where You're just walking around and can fight someone else? Or instanced PvP like arenas or BGs?
Diablo II PvP occurs in the normal game world. In the party window you can "click to go hostile" with another player or group of players. This can only be done in town. Once you've done that, you can attack each other anywhere you find yourselves in range, as long as it is outside a town. Organized PvP usually takes place in the Blood Moor, right outside the main hub in Act 1, the Rogue's Camp. But, I've been almost anywhere in a public game and had someone go hostile, and then you have to decide whether to Town Portal to safety, or take your chances. This is one of the benefits of a private game; you won't get random Player Killers coming in to amuse themselves.