Fridge, the fear is that Iraq will immediately deploy WMD, whether it is nuclear, biological or chemical. Nuclear and Chemical have immediate and lasting effects. This would put our troops in the position of fighting in a contaminated environment.
They (Iraq) have only this option available to them because they cannot match us militarily with conventional weapons and tactics. I am just a sillyvilian. If I see and understand this, I can only imagine what the actual military plans are. I would guess that they are making the assumption that the environment will be immediately contaminated by the Iragis upon commencement of hostilities. Everybody will be up to speed on survival in a contaminated environment, and will have (hopefully) trustworthy and functioning MOPP gear.
To get a feel for this, see if you can get ahold of a full set of MOPP gear (boots, pants, jacket, gloves and mask with hood) and do jumping jacks for 30 minutes nonstop in 90 degree weather.
A little hint: MOPP gear is quite effective as cold weather gear.