A war in North Korea would be very different from a war in Afghanistan, it would in this case actually be closer to a liberation than an occupation - while the communist state controls the country in a dictatorship the majority of the populous is not communist. Look at the states of the Iron Curtain for a similiar example, they wanted out of communism.
Also for the person saying brinkmanship - you're right but it's one sided brinksmanship. North Korea is being provocative - possibly due to internal politics with the ill health of Kim Jong Il, South Korea isn't being particularly provocative.
China is in a tough position, if North Korea pushes too far they will not have the international political capital to defend N.Korea - they rely on being reasonably friendly with the West for trade. However they really don't want South Korea - a fairly liberal democracy - right on their border, which essentially what will happen if the N.Korean state fails.
It's going to be interesting, it all really depends on what this young man they've essentially chosen for succession is like. If he's as nuts as his father then I can't see N.Korea lasting, it's already bankrupt and starving.
Edit: And invading N.Korea without even more significant provocation than this would be insane. It would need to be a bulletproof and undeniable casus belli. Something like a military attack on a S.Korean city. Something that is so absurdly provocative and undeniable that not even China can justify defending N.Korea.
