Ketsueki,I gather that the going wisdom was that Saddam was making and had made tonnes of WMD's.Now,WMD's happen to be a tool any terrorist would love to have(imagine what would've happened if the first plane diving ino the first tower had a nuke inside).It was thus argued that if Saddam(a WMD possesor who hated America) got a hook up with Osama(a terrorist who equally,if not more,hated america),the results would be,uhm,for lack of a better word,I'll use disastrous.
Now,the WMD's are a story we're now familiar with.
Plus what Pony said above.
And as an aside,can you see why I'm laughing when Hammurabi asks "...who cares about those supposed weapons of mass destruction?..."?
Aaahh,those!! :p