I have lived in PNG, Port Moresby & Mt Hagen and the following is true....
*As a foreigner you live there AYOR
*You will live in a compound secured with barbed wire
*AirNG crew live in such a compound
*Yes, gangs do roam the street with guns
*Foreigners are a target
*In many places alcohol is banned, if you have it they will kill you for it
*If gangs access your property to steal they probably will kill you if you are there.
These are all true stories and do happen. Port Moresby is probably the most dangerous place to be in PNG. These things probably wont happen to you but I have to stress the dangers associated with living there. These things have happened and continue to happen. Other parts of PNG are fine and PNG people are lovely. There are just gangs that take over and there isn't much rule there.
The good side is there are many Australians living in PNG and loving it, you just have to be aware. I'm just laying down the facts.