The US and Russia seized 99% of the nuclear materials that existed in the former USSR outside of Russia in the 1990's. As for being able to make nuclear weapons out of just about anything, you're right. Know what a major byproduct of fission power is? Neptunium, which only needs a C-Mass of 7kg. What would the ensuing explosion look like? I have no idea. But yeah, not hard to make nukes. Unfortunately with nuclear proliferation proceeding at its current rate, with numerous countries being inundated with nuclear materials (Venezuela, N. Korea, Iran), and the ability to refine them, I believe that a large nuclear deterrent provides a positive field of play so as to discourage manufacture of nuclear weapons. Along with the deterrent, there is also the UN, which provides a stop gap via inspection. That's not to say that if a person or persons really wanted to build a nuclear weapon that they couldn't. I'm just saying that the threat of wholesale nuclear retaliation is a definite possibility, and I'm not even sure Osama Bin Laden would be willing to put the people around him (Afghani & Pakistani) at risk like that. Most of what I'm saying is a broad sweeping generalization, but I believe it's in the ballpark.