Here's my scenario:
First, there's no doubt in my mind that the US knows exactly where Sadam is keeping his NBC stockpiles, manufacturing facilities, etc. This is based primarily on our increased intelligence gathering abilities, advancements in satellite technology since the Gulf war, and, of course, Israeli intelligence...
For the first few weeks, inspectors will go to run of the mill sites for inspections and will be allowed unfettered access by the Iraqis, since both sides already know there's nothing illegal to be found at these sites. This will be done to allow the buildup of US troops and supplies. Once things are in place, the inspectors will be directed (based on US intelligence) to inspect sites known to have NBC weapons. Iraq will, of course, deny access for obvious reasons. Thee US will then return to the UN Security Council and provide proof that not only are there NBC weapons present at these sites, but also the fact that they were denied access by the Iraqis. After that, its all fair in love and war.
IMHO, I don't think the US would have modified the resolution to require a second meeting of the Security Council before military action can be taken unless the US knew they could provide the proof necessary for the UN to sanction military action.. my .02 cents..