I'll start by saying I can understand where others have gotten the interpretation that ITNW ignores AP. I don't agree, but I can see how you can arrive at that conclusion. Also, I have to echo the earlier point about doing what's right for your table and game experience. Who cares if it's right or wrong so long as it's fun.
That said, I'm going to argue a few points.
QUOTE (Lanlaorn @ Jul 1 2010, 06:08 PM)

Because it works the other way around, they need to specify it DOES work (like the Hardened Armor entry does). Also IMO they even did say it doesn't count as armor by constantly putting armor in goddamn quotation marks! What do you think those are in there, just for decoration? The whole entry screams "when comparing DV to see if it bypasses this, this is NOT normal armor" and then they had to specifically say that for damage resistance tests it IS normal armor. Why would that sentence be included if it's normal armor all along?
Actually they do not need to specify that AP does work. They DO however need to specify that it DOES NOT.
QUOTE (SR4A, p160 OTHER COMBAT FACTORS)
Unless otherwise noted, the following rules apply to both ranged combat and melee attacks.
This means unless a spell, power, item, etc,
explicitly grants an exemption it is, by RAW, using these rules in ranged or melee combat (I can't think of any physical combat that isn't one of those two, and we are only looking at physical combat in the case of ITNW). The very first heading under that section is the rules on Armor. And those rules include Armor Penetration.
The description of Immunity must be read not just as a description of Immunity To Normal Weapons, but rather as
Immunity. The term Armor as a game mechanic term does not encompass all the possible Immunities, such as Age, Poisons, Toxins, Mind Control, what-have you. As such, the writers used "Armor Rating" to denote a mechanic that CAN be used as either Armor or as a Rating used in other manners, such as with Age.
QUOTE (Immunity (partial quote))
... This Immunity Armor is treated as "hardened" protection (see Hardened Armor above), meaning that if the Damage Value does not exceed the Armor, then the attack automatically does no damage. ...
In this statement they once again use the term Armor, without quotes. Without quotes, Armor has a defined game mechanic associated with it, found on SR4 p160 which is directly beneath the quote I provided saying that unless otherwise noted the following rules apply.
Also, for clarity's sake they should have used the term "Effect" in place of "Damage" in the description as not all forms of Immunity are granted towards things that cause damage. Consider Immunity to Age... where's the "Damage"? Obviously we use the rating vs. rating, but really the misuse of terms creates confusion, and this power needs far less of that. Truly, the whole thing needs a re-write.