The Mullahs ain't stupid..
Then why persue nukes? They have to know the US and Israel won't let it happen. I have no idea if we know where Bin Laden is, or not. My instinct tells me we have a pretty good idea, but cannot act on it for various reasons:
1) It would expose intelligence assets.
2) If he's in Pakistan, action would damage the relations with Musharraf and risk conflict with an Islamic nuclear nation.
3) If he's in Iran, action there would risk having an unsettled Iraqi Shia turn on American forces. It may also galvanize nationalists in Iran to support the current regime.
4) The intelligence is there, but the CIA's credibility is tenuous after Tenet's "slam dunk" claim.