I had a game the other day where Saladin headed the UN and passed a resolution barring nuclear weapons. The only problem is nobody discovered fusion yet, none the less built the Manhattan Project. My question is: Like the SDI, should the no nuclear proliferation treaty require someone to complete the Manhattan Project first?

I suppose logically it could make some sense; you know that they're a potential threat even if they're not a realized one, and you don't need to know the exact form they'll take to know that you want to outlaw them. The SDI needs to know exactly what it's shooting at to realistically shoot down a missile (insofar as it's at all realistic anyway).

My only complaint for the nuclear game is that there's no penalty for building SDI. Could make things rather more tense if there was a penalty (especially a diplomatic one) for it... in real life nations don't start down that path for the most part because a functional SDI operational when your enemy doesn't have one means you have first strike capability, which throws the whole balance of power in the world off.

Of course, actually pulling it off so that you had an incentive (or could be given incentive by other nations) to not build the SDI, I'm not sure how that would work.

Simple.... SDI is also banned by the Non proliferation treaty as well
or
SDI=Diplo penalty for all civs with Nukes