Iran wont do anything. Even if they had a bomb they wouldn't do anything. The threat of mutually assured destruction is enough to keep them from doing anything stupid that would exterminate their countries citizens in 1 fell swoop. Look at pakistan and india? Both technically at war, neither country using nukes to blow each other away. Look at the koreas? Both nuclear armed, neither making a first move to launch nukes.
The one I worry about is Israel. They are a pitbull unleashed. More likely to bite first. They are the ones who seek war. I think Irans leaders talk alot of smack much like saddam Hussein. I don't think they can afford to do too much right now with the sanctions and other things that are pushing the country into poverty. If Israel strikes first, I can promise you that will be WW3. Other arab states won't allow it. Russia and China will immediately flood Iran with support from weaponry to supplies. The US will be forced to get involved dragging us into another war. Let's hope washington tells Israel that no premptive strikes....