This Der Spiegel article has the details:
Hear that creaking sound? That's the kinks straightening out of ol' V. D. Hanson's love sausage.
It's entirely likely that, not unlike Ahmadinejad's weird hortatory jabs at Israel, this is somewhat for show -- for now. As Bush has already pointed out (and was actually correct in doing so), all options are on the table. Right now it's unrealistic because Russia and China have already registered their serious disapproval of such a pre-emptive strike. And we're no longer in a position where we can just unilaterally give the finger.
So chances are that the next move is actually up to Iran, whether they want to keep fucking aorund in their theatrical attempts at nationalism, or if they're going to settle down. It might not hurt to reach out to them through the Euros, but that ain't gonna happen. So we do our little dance.
This is where it gets a bit scary. Now, we know beyond a shadow of a doubt that, prior to 2001, al Qaida had hooked up with the governments of Afghanistan and Pakistan. We got Pakistan to reluctantly cooperate, but there's every sign that many elements of the military and intel agencies there may still be covertly helping al Qaida in general, and bin Laden in particular.
Then you have the Bushies' assertion that al Qaida was also in cahoots with Saddam Hussein. So, by the US goverments estimation, that would have been three national governments that al Qaida held some sort of sway over.
And now Iran, which would be four governments supposedly in the thrall of a terrorist gang. This would be suicidal on Tehran's part, and they know it. There's simply no upside for them to be involved with al Qaida, and risk being found out. (Though again, there has never seemed to be any real urgency about weeding out the pro-al Qaida forces in Musharraf's army, even though at least one of his top generals, who had breakfast with Bob Graham and current DCI Porter Goss on the morning of 9/11/2001, had been found to have wired $100K to Mohammed Atta.)
Here's my best uneducated guess. Former Afghan "freedom fighter" turned Taliban asset Gulbuddin Hekmatyar is known to have a base in northern Iran, where he goes back and forth across the Afghan border with impunity. Tehran lets him because, well, he's a religious whackjob fundamentalist warlord. But we've probably had the opportunity to take out Hekmatyar in Afghanistan, but like most warlords there, he's got his base.
This is speculation, I'll admit, but it's damned odd that this supposed al Qaida connection in Tehran is being bandied about. This administration ran out of "wolf" cards long ago, so we'll see where this leads.