Colin, you ask "Why can the US have WMDs and not anyone else?"
The US doesn't go around gassing people for the hell of it. Yes, we have WMDs - a helluva lot of them - but we don't use them say, like Saddam uses his. Gassing his own people for the simple "fun" of it.
I guess "responsible use" would apply? Not that there can really BE responsible use with weapons like that, IMHO.
I've heard from a couple of different places that Iraqi forces have been seen in full chemical suits setting up 50-gallon drums of something (they don't know what) in the path of the forces in the North.
If they're in full chemical suits, what's in those drums? Could be just psychological warfare, but then again...