Their bomb is too big to fit on their missiles. It will be many years before they are able to miniaturize enough to put a nuke on a missile. Their only possible means of delivery at the moment is by boat or plane, either one of which is certain to be intercepted leaving their nuke and incontrovertible evidence in the hands of those they intended to attack.
What they will do next is launch ICBMs over Japan and towards the US and say nothing. A form of terror whether they have the true capability or not. This would make the U.S. (Bush) appear very weak as we would continue to let him do so. Bush either gives the Chinese time to act or we must take them out or we do nothing.
The Pakistani bombs fit on THEIR missiles, and Pakistan sold their compact bomb designs (Chinese origin) to all of A.Q. Khans clients, including NK. There is nothing secret about even a lightweight bomb, sub-1-ton, that is a reasonable payload for a Scud-derivative, or the other missile designs NK has. It is not safe to assume that the NK's do not know how to make a deliverable bomb.
The knowledge is out there. All anyone really needs is enough Plutonium.
If they shipped the other 10 nukes in shipping containers to our ports several weeks ago....well this could be an interesting few days.
Thanks Carter and Clinton, you screwed us again.