I expect a lot of the delay is due to preparations to deal with all the terrorists who will 'show their hand' once we attack Iraq. We need to be in a position to kill them all.
We will be fighting a localized 'hot war' (Iraq) and a worldwide undercover war of assassination of terrorists. (IMO)
I also think some of this is somehow related to the death of Abu Nidal. And This
"A top Iraqi Kurdish official said Wednesday that Arab radicals linked to al-Qaida were experimenting with chemical weapons for terror attacks in a laboratory in a remote part of Iraqi Kurdish territory."