7h15 r 7h3 b357 5h0w Evar, p1zzzzz dun c4nc3l

Without going into too much detail:
It is called "1337", or rather 'Leet Speak', which is what some weird computer gamers use. To be 'Leet' is to be Elite. An Elite is someone very good at what they do, with the term in this particular context originating among Hackers in the 80s.
Certain gamers adopted it ("because it's cool, ja!"), along with a variant of the Hackers' cant and it has become popular among the younger players. It's like text speak (txt spk) on your cellphone.

http://en.wikipedia.org/wiki/Leet

So when they talk about "Pwnz u noobs, I haz skillz", or something like that, they're telling you they spend all their time ignoring their education and the real world in favour of wasting their life on computer games.

I don't understand it, myself. I've been gaming since the Spectrum 48K (and have spent time hacking and phreaking too) and am still putting a good 30-40 hours a week into some of the latest games. I geek out with the best of them... but I've *never* felt the urge to talk like a mentally challenged LOLCat!!