The new president of Iran has a point when he suggests there is
a double standard when it comes to the scrutiny given to Iran's nuclear program versus that given to Israel's probable possession of nuclear weapons. I would agree that at some point, Israel should join international non-proliferation agreements and that its possession of nuclear weapons should become more of an issue than it is now.
That said, I think it's important to realize that part of the world's acceptance of such a double standard is the recognition that Israel faces a unique existential threat for which there's no real comparison among other countries. I think that any agreement on Israeli nuclear weapons would have to be in the context of a broader Middle Eastern peace agreement that provides guarantees for Israel's physical security.