The ROK military forces are quite formidable and very advanced techwise.

They would make short work of the DPRK's ground forces, but seoul would pay the price in the early phases of any conflict.

Seoul would likely not be attacked unless there was implicit strategic reason to do so, such as mounting and irreversible loss.
Remember that war is not a game of absolutes - the point is not whoever is completely annihilates the other first wins. North would likely only begin a war under extreme duress [relative, mind you] or to take South Korea's economic might to integrate it into its own. Bombarding Seoul would then be a useless gesture.

From there on, let's discuss logistics. In all likelihood, North Koreans would find it difficult to man a ground assault. The DMZ, in addition to American and South Korean artillery and defensive measures [mines, etc] would make that effort suicide without several days or weeks worth of fighting. They could try and take numerous safe routes presently used for economic cooperation between the two countries, though its highly likely that such routes are already planned for destruction by allied forces in the event of a war.

Which essentially leaves North Korean soldiers to trek by foot, or bunch together in large convoys. My guess would be the former.

The NK airforce is largely ineffectual in any conventional role, so my guess would be they would supplement artillery in delivering WMD's. Likely biological and chemical, to enemy soldiers and none-essential civilian centers.

Navy is a moot point.

The issue is neither side can win and gain anything meaningful from a war. The North would die, utterly, if they attacked.
The South would achieve a broken capital and hundreds of thousands killed if they did so. And for no apparent gain. [What are they going to do, commandeer that raging NK industry?]

No matter how begins the war, both sides will lose.

[edit on 22-4-2009 by Iblis]