When I got my Beetle about a two months ago (it's a 2000) the horn wouldn't beep and I wanted it to. My friend is a VW mechanic and activated it using his computer and OBDII. It's a very quick procedure, a few minutes. You can have it deactivated the same way, but I suppose if you don't personally know a VW mechanic than you might have to go to a dealer. There are no fuses to deactivate the horn only.
As for the security sys, I'm not sure that would be a good idea. I believe the security system might work in conjunction with your coded ignition key. I would verify that before removing fuses for the security system as otherwise your car wouldn't start.
Hope this helps!
