First Person View
Repeatedly save and load the same saved game and the view will eventually switch from third person to first person view.
To go to first person view, press L3. To revert back to normal, press it again.
Contributed By: Anonymous.
How to enter cheat mode
Whilst playing the game, press X to bring up the menu, then whilst holding down select push the left analog stick to 12 o'clock then rotate it clockwise 3 times (all the time holding down select) and then anti clockwise 3 times. You should find you now have a new Icon underneath the message log which allows you to turn on infinite health, ammo etc as well as level selecters.
Contributed By: mezcal.