Appearing desperate and crazy is a national policy of North Korea that they have used for decades. It's not a very hard sell, either. I don't imagine that they are any more crazy than usual. They may well be more desperate, but that is only because North Korea has no effective patron state, no way to sustain its operations independently, and a very powerful enemy that it has been irritating for almost 60 years.
You're right in that it is mostly an act; the North Korean leaders are calculating and methodical, often incompetently so. They are also walking into a trap.
Bush's point at the U.N., to be made sometime this summer, will be that if North Korea is desperate, it is their own doing. All they have to do is get in line with the international community, blah blah blah, and we'd help them out. He'll throw cash, food and oil on the table, and he'll ask for some concessions that will sound rather bland and appeasing. The right will gasp in horror, the left will cheer, and the North Koreans will accuse us of being despotic aggressors, refuse entirely, and storm out.
Cue the U.N. sanctions, cue the USN blockade. Past that, it's war or collapse for North Korea.