This will only work on the PAL version of the game.
First make sure the game is set to 50hz (this is crucial).
If it's set to 60hz then take your memory card out before you boot up the game, set to 50 .. then re-insert at the title screen.
Anyway... just load up your game or start a new one.
In order to do the superjump you need to have a stick or a sword equipped (will also work with lightsaber).
Start running in any direction and do a running jump.
Right after you hit Triangle, hit Square. The timing needs to be really exact.
If executed properly you'll see him fly farther and one 'block' higher than he normally would.
Keep practicing the jump, it will come in handy when you'll need to get to Yorda quick.
....You can also skip major parts of the game with this jump, I won't tell you where... but just have fun with it, explore.