Is it (8) nuclear weapons or (10) nuclear weapons now, that the CIA and other agencies theorize, that the DPRK possesses, to Iraq's zero (before and after the war?) Please clarify.
With regard to Iraq, nuclear weapons aren't the primary concern, although they might have been in the possibly near future. The primary WMD problem with Saddam was his known use, development and stockpiling of chemical and biological weapons coupled with his allainces, overt and covert, with numerous terrorist groups including Al Queda (yes, there was cooperation before the war).
Added to this was Saddams know intention to exact revenge on the U.S. for the '91 Gulf War. This included the first Trade Towers attack in which his regime was complicite and the overt attempt to assasinate a U.S. President. The possibility that he might supply chemical or biological weapons to terrorists to these ends is more than sufficient.
Most people are terrified of nukes. If they knew the relative effects of the three major types of WMD, the nukes would be at the bottom of the list. As a former MI Army officer who is well familiar with them, and whose daughter is chemical warfare specialist in Iraq right now, I'd rather be nuked than exposed to chemical or bio weapons.
As for North Korea, Kim Jong Il is reletively contained. He may have nukes, but he's not going anywhere with them and he knows what would happen to him if he nuked the South. He is not likely to be able give them away to terrorists, because he has two major superpowers on his doorstep to keep him in check. Even if he were inclined to send them to terrorists, he couldn't do it easily. His two land borders are locked tight, and we track everything that comes and goes by sea and air.
Iraq, on the other hand, borders five countries with very porous borders and occupied by people who don't like us very much. Getting a WMD out of Iraq and to the U.S. is far easier than getting one out of North Korea.
You can jump up and down about 8-10 nukes versus 0 for Saddam all you want, but that argument is straw dog that won't hunt. It sounds good until you break it down and analyze it, but all it is is a meaningless sound-bite. But some people just can't resist the numbers game.
As for the follow-up argument about not finding chem or bio weapons in Irag, that also is not true. There has been plenty of evidence of his bio and chem weapons programs and the munitions to use them. It is very easy (reletively speaking), to dispose of these weapons. The equipment to make them is dual use. Remember the bombed "baby-milk" factory of the first Gulf War? It did make some baby-milk, it also produced bio-weapons, a fact that was confirmed by the U.N. and which was conveniently forgotten in the interests of bashing the US. Numerous such facilities, recently (as in the last five years), have been identified, not to mention two mobile labs that had been scrubbed so clean that no trace on anything could be found in them. Saddam had plenty of time dump the weapons or get them out to Syria.
Then there is the side benefit that invading Iraq produced in Libya. As it turns out, they were much further ahead in their WMD programs, particularly their nuclear program, than anyone had thought. Ousting Saddam convinced a state supporter of terrorism to stop and play nice.
In Iran, a country that is run by avowed enemies of the United States, they are already on the verge of being able to produce nuclear weapons (they also have chemical and biological weapons, some of which they used against Iraq during that war). Ousting Saddam gives us bases from which to easily strike them should they try and do something stupid. They are now bracketed along two of their borders by countries occupied by U.S. troops. Their ability to move WMD's in and out of their country and into the hands of terrorists has been severely hampered.
You will also recall that Hezbolla, a creation of the Iranian regime declared war and Jihad on the U.S. after the First Gulf War. Iraqi newspapers prior to the latest invasion of Iraq called for muslims everywhere to wage Jihad on America and it's interests everywhere they could be found.
When deciding which threats to eliminate, you first have to determine where the real threats are (the guy with the biggest gun or bomb is not always the biggest threat). Then you have to decide which threat, when eliminated is going to return the most benefit.
Kim Jong Il and his nukes are not a serious threat to the U.S. Saddam was and his chemical and bio weapons was. The return on eliminating Saddam for both the near and far term was much greater than would have been the return on trying to invade North Korea to take Kim's saber away from him.