Just did this myself and could not believe how easy it was.
I can't guarantee that the following will work for you and it did for me.

-Download the ISO:
http://www.megaupload.com/?d=IP0KD0O0

-Extract and Burn to a CD:
http://www.imgburn.com/
I did the burn at 8x, slowest setting the laptop would do, avoids error on CD

-Open door and trunk, switch key in ignition to position 1.

-Let the NAV boot up.

-Go to the trunk, eject the NAVIGATION DVD, put the CD you just burnt in.
Leave your door and trunk open, apparently voltage spikes are not a good thing while doing the update.

-Follow instructions on the screen, in a a few minutes you will be done.

-When prompted eject CD from trunk, your NAV will reboot, put NAV DVD back in.


Don't switch the ignition off or mess around with anything that pulls power from the battery while doing this. Keep the door and trunk open as well.