This will seem inexplicably complicated for no reason, but this is how Infiniti and other car makers have changed the way HID headlights are replaced. The low beam bulbs must be accessed from behind. There is no way to access them from under the hood. I did this myself on my previous M, but on my curent 09 M I paid the dealer to do it (one hour labor charge).
1) jack up the car and place securely on a jack stand
2) remove the front wheel
3) remove the inner fender clips to allow you to bend the inner fender liner out of your way
4) look for the door that allows access to the low beam headlamp bulb
5) twist the door to remove it and expose the back of the D2S bulb
6) remove the harness and a metal clamp that holds the actual bulb in place - release it as shown in the video below
7) put on CLEAN gloves and wipe the new bulb with an alcohol swab even it was taken directly out of the packaging
8) the new bulb will only fit inside the socket one way to prevent misalignment
9) reconnect the harness and return the metal clamp to it's locked position
10) replace the plastic door to keep moisture and dirt from the bulb
11) IMPORTANT *** test the bulb to be sure it lights
Replace the front wheel and tighten as you would if you replaced a flat tire and then fold the inner fender liner back in place.
Replace the fender liner clips, lower the car, and finish tightening the wheel.
To remove the clips, pop the center pin portion outward first, then pull the main clip free. To replace them, make sure the pin is still in the outward position, place the main section of the clip in place first, then push the pin inward to lock it in place. If you damage a clip, they can found on Ebay for very little money.