First of all, WW3 is already happening, but it is unlike any war we have ever fought, one very much occurring "below the radar." Our enemy is a medieval, obsolete mindset which is determined to destroy all that which does not conform to its limited, infantile, ranting, foaming-at-the-mouth view of the world.
The real fear regarding Iraq (not the manufactured one by Bush & co) is that, as a terrorist state, it had the finances and hardware to develop a nuclear weapon, but not the delivery system. Terrorists provide the delivery system. Iraq, however, has been taken out of the picture...but Iran has not.
They Will build a bomb, and they Will use terrorists as their delivery system. I say "will" because this is a scenario we Can Not afford to think otherwise on. Comparisons to individuals (as in an above post) or discussing this in abstraction does not do justice to the potential physical, psychological and financial damage a nuke detonated in a city will cause.
My guess is, within the first quarter of this century, someone Will get nuked. It is almost inevitable. It may not be NYC, it may not even be the US, but some country Is gonna get hit (could well be Israel).
The state of affairs our world is in sucks big time. It is horrific having to send brave young men and women to fight a war and die, especially as a preventitive, pre-emptive measure. But if we don't...the far, far worse is yet to come.