I disagree with the etymology listed for "pwned." It's origin was most likely in multiplayer games (which is very common for l33t speech), though perhaps borrowing from *nix/hacker-speak. The substitution of the "p" for the "o," however, is almost certainly a product of multiplayer games. After a particularly humiliating kill, a player could be said to have "owned" the other player. The o-p transformation then would either be an accidental mispelling that becomes intentional (the "o" and "p" are next to each other on a QWERTY keyboard... see the use of 1s for exlamation points to mimic hurried typing: pwn3d U!!!!11!1!) or an imitation of part of a smiley (the p, often used in conjunction with a colon for "eyes" or a semicolon for "winking"), usually standing for a tongue sticking out (:P). Neither of these modifications make sense in the context of hacking, but they make perfect sense as part of evolving terminology in a frantically-typed multiplayer game.
This is Free Republic, people... let's make sure that even the little things are correct! *grin*
I'll admit it:
That was definition number 6 in Wikipedia.
I just get a kick out of reading geek-speak that someone actually thought would be understood by the rest of us in the masses.