It took the US and USSR over a DECADE to go from first detonation to low-yield atomic shells. It took years even to make them something that could be carried by any but the largest aircraft. With the resources of the world's two richest nations, no international pressure to restrict developments, and no nations threatening war over testing (miniaturizing the warhead is exceedingly difficult without such tests.) IF the DPRK has any serviceable nuclear warheads, they will likely be very low yield, and it is unlikely that they have any delivery system besides their upgraded Scuds. The bomb would probably be too large to be carried by most of their aircraft, let alone their artillery. Those missiles have been brought down successfully in the past by SAMs of the type used by UN and ROK forces. (The "bullet with a bullet" applies to ICBMS, which are several orders of magnitude more difficult to engage do to speed.)
EDIT: Euginator, It IS an inherent nature of the technology. For an implosion-type bomb, the core MUST be compressed exactly right, or it can't detonate. Similarly, a gun-type warhead requres the driver to strike the stationary portion exactly.
As to their conventional capabilities, they are FAR more advanced than most of you seem to think. The most advanced equipment they are known to possess (such as the Mig-29) is nearly at par with the F-15 and F-16 fighters deployed in theater, and their second-line equipment (such as Mig-21 and -23 fighters)is servicable and in very large numbers. Unlike Iraq, the equipment will be in extremely good condition, operated by highly trained, highly skilled soldiers. A second Korean war would be a long, protracted ground war, with perhaps as many as a million casualties.