Following up this Calpundit post, I don't actually believe the administration believed that Iraq had any kind of WMDs which posed a real threat to the US or anyone else. I think they assumed Iraq would have something which could be used to justify that claim - some nasty chemicals, say. But, some nasty chemicals are far less of a "WMD" than our shock-and-awe (ah, remember all the media whore oohing and aahin over those. sick, really.) conventional bombs are.
As one of Kevin's commenters notes, "it was completely obvious the administration did not believe there were WMD as there was no plan to secure them (or anything else for that matter) and insufficient personnel to do so." This is correct. If they truly believed that something existed, and truly cared about the "war on terra," there would have been a bit more concern about such things either being used on then-Viceroy Garner's new digs, or falling into the hands of international terrorist organizations.
And, one final word on the whole "they never said it was imminent!" nonsense. When there is a country which has been explicitly the enemy of the US and one of our major allies for years, and when the Vice President says about the leader of that country "Simply stated, there is no doubt that Saddam Hussein now has weapons of mass destruction. There is no doubt he is amassing them to use against our friends, against our allies, and against us," I and every other rational person would conclude that there is indeed an imminent threat. I mean, what the hell kind of weapons of mass destruction are they if they a) exist, and b) are not a threat?