As has already been said, FSX still
remains a sanctuary for non-combat flight for those that want it. You do not have to install this - or tacpack. Indeed you have to pay money to add the functionality. Don't spend the money, don't click install, your sim stays safe and civilian.
As I said before, my fear is when this functionality hits multiplayer. Then we have teh kidd13z with thehr u83r5n1p3r skillz flying around shooting down 747s flown by people who just want a peaceful life, "coz itz fun an u r sad 4 not doin it". As long as it stays only on the PCs of those who want it, I have no real problem with it.
That said, this is still quite an early incarnation of what is required. Lewis has found the SDK documentation for me (thanks Lewis!) and... it didn't help me at all, trying to add weapons to a different aircraft. I had to hack through the XML code by hand and I hope I haven't deleted something critical. I then still need to zero the guns, even if this works.
As Bjoern says, though. There's nothing gained by doing this at the moment, other than making AI aircraft vanish.
P.S. I broke the XML. The guns I just painstakingly edited in don't work.
Ian P.