We should do absolutely nothing. First off, most of the "North Korea is going to bomb *insert country here*" news is simply sensationalist crap.
Second off, USA can't really do anything. In order to move troops into North Korea, they will have to go through China.
Now, America is in quite a large deficit. We have been running a negative trade balance for too long now, and the Iraqi war has drained our coffers. The only country that is significantly helping us climb out of the financial blackhole that we are in is China. Quite a number of Chinese businesses are relocating to the US and China is pumping money into the US economy through the purchase of government bond.
Thus, if Obama does make the decision to send troops into North Korea, he will have to ask China, unless he wants to risk a worsening of the economical crisis.
China will assuredly say no, as I am sure they are not too keen to have their nuclear weapon toting neighbors declare war against them.
If, however, China does allow this military maneuver, then I believe we will be on the brink of WWIII.
I know not with what weapons WWIII will be fought, but WWIV will be fought with sticks and stones. - Einstein.