First comment: it's the usual agressive rethoric of that regime. Just have a look there http://www.kcna.co.jp/index-e.html
I don't think there is much to fear, they are just barking as usual.
Second comment: it may be also related to this : http://www.globalsecurity.org/military/wor...-jong-woong.htm
Obvioulsy, Kim Jong Il health issues are more serious than thought before. In such totalitarian, with one-ruler, it is not safe to choose a successor, unless you want to be overthrowned (killed, coup, whatever) by the said successor. But, if you are close to death... So, they are busy in Pyongyang, as the Invincible Feldmarshall might die, and they are just saying to Seoul: mind your own business.
In no way, by the way, is the DPRK able to start a war, let alone win it.