If you need to refresh your memory on all this stuff, last year I wrote a quick summary (with links) of all the 2003 activity here.
FWIW, this is one of the reasons I've never quite bought into Matt's "incompetence dodge" idea that success in Iraq was never possible. Sure, we couldn't have sent 500,000 troops, but we could have sent 250,000. And we could have made serious postwar reconstruction plans. And we could have stopped the looting before it spiraled out of control. And we could have reconstituted the Iraqi army and limited de-Baathification to only the highest echelon of Saddam-era officials, as the administration unanimously agreed to do until Cheney and Rumsfeld unilaterally overturned the decision. And now we can add to that one more thing: in the aftermath of our lightning victory in Iraq, Iran really was feeling some pressure and was willing to talk to us about halting their bomb program and possibly cooperating in other areas as well. If you take all the stuff above, and add to it the possibility that the Iranians might have been maybe grudgingly, maybe unreliably, but still willing to use their influence to help us out with Iraqi players like Hakim and al-Sadr, who knows? Iraq might not have turned into a triumph, but there's a good chance it would have gone a helluva lot better than it has.
But like Matt says, the Bushies couldn't take yes for an answer. So we are where we are.