The last anlysis of the Iraqi armed forces I heard was that about 50% would either surrender, turn on their leaders or run.

Of the remainder, about 25% Republican Gaurds, would fight. But they have not been seriously resupplied for ten years now.
No spare parts, munitions depleted from ten years against Iran, and the coalition in 90-91. Outdated equipment, poor unit cohesion, shaky command comunications.
They already know their T-72's can't go head to head with an Abrahms, and they have no air power worthy of the name.

It will not be a cake walk, but it won't be landing at Okinawa either.

Most likely scenario would be token resistance in the open, serious resistance in cities ETC. Urban warfare is slow and bloody. Given our reluctance to use indiscriminate bombardment this means some foot soldiers will have to do the nasty work of building to building clearance. Which means civilian casualties would rise dramaticly, Saddam has a history of useing innocents as shields.

And that would be the easy part, putting Iraq back together in an acceptable form would take years.
I am still on the fence about Iraq, while I believe Saddam has to go, is he such a threat that we destroy a lot of carefully nurtured relationships with other nations around the world?

We need more information, has Saddam actually manufactured more N/B/C weapons. Can he deliver them, is he a clear and present danger to us. Like al-Quieda or some of the more obscure terrorist groups.
While there are al-Quieda in Iraq, there are not many. And they are running, not cooperating with the Iraqi governement. Even now, as calls for action against Saddam from some government officials are in every newsport, no one says that al-Quieda is working with Saddm.