Severe Punishment threat to North Korea

Simply put: What severe punishment will North Korea face if they conduct an underground nuclear test?

Close allies, Russia and China, have made note that North Korea wants to prove their nuclear capability (Sept 10, 2006). North Korea is just about out of friends and has been on a collision course of some sort for some time now.

So, what will happen if they detonate their test? What is the severe punishment the world nations are discussing? What would Russia and China do? Can you help give me a clue?