Will North Korea attack South Korea?

If so, with or without nukes?

Answer to both questions: God knows. The leader of North Korea is insane.

It is normally assumed that anyone who wishes to use nuclear weapons simply to frighten or deter other nations would want to test one in the open. This is not a firm rule...as far as I know Israel has not publicly tested a weapon. But we may have that much warning. There could be a bluff going on too, but if so, it's a damn good one.

What would the South Korean response be in either case?

Well, I assume that an attack by North Korea would warrant a military response. Even Davin supports self-defense after the damage is done. Big question is who would respond besides North Korea? I assume the U.S. has little choice in the matter, and would enter the fray. Would Japan come in, even in just a support mode? Or sit it out and hope NK doesn't lob missiles its way? And the $64,000 question: what about China?

Will the current régime in North Korea survive the next decade (in the absence of war)?

It's lasted this long. Don't see why not, barring incident of course.

Will the population of North Korea revolt against the Kim Jong-Il government?

No. The army still works for the Fearless Leader. The army might mount a coup, but I'm not sure what that would accomplish.

What should the USA do in the Korean Peninsula?

Everyone wants us to step out in front and negotiate with NK unilaterally (NOW they want unilateral). This gives the rest of the world the usual opportunity to throw rotten tomatoes at our backs while we take enemy arrows in our chests. But we need to insist on bringing at least China in on this. North Korea is basically a Chinese client state, and they should be cleaning up their own mess. Hell, most of their nation is in missile range too.

It would be really nice if we could buy them off or convince them that they can't win a confrontational battle.

Near term, I think a good case might be made for pulling our troops back from the DMZ some distance. At least to Seoul, or maybe Japan. Replace them with a carrier in the near vicinity (I think the Carl Vinson is already there), and other air and naval power at the ready nearby. A LOT of Patriot missiles, and that laser cannon in a plane if it was ready. These could respond rapidly in case of an attack--taking out all that damn artillery--and probably more effectively. It ain't 1950 anymore, and while I'm no tactical expert, I'd bet we don't need soldiers on the ground to rapidly repel an organized attack force, at least not at first.