<a href="http://www.spacewar.com/2003/030603054417.8lg8lqpn.html"; Look Here

The WW2 Nazi V1's had everything except a GPS and did a good job, compared to their design specs. I can't imagine how this bloke could fail in his goal.

Fortunately, Australia is more than 100 km away from NZ. Come to think of it, most of the civilized world, and all of Australia, is more than 1,000 km from NZ. Some parts are more than 10,000 km away!

So no immediate panic, but the same general hint. You can build a crude dirty N-bomb in your kitchen, and a cruise missile in your garage, but homestly, why bother when you can have a more reliable impact by shipping in a container-load of C4 with some radioactive waste...

(Caution - I do not condone any of the above. I merely point out its simplicity)
Who is in charge of stopping this stuff? - F*$# Knows!