Iranian President Khatami attacked the idea of a US war against Iraq forcefully while in Spain this week.
Officially, Iran has all along loudly denounced the idea of a US invasion of Iraq. . The ruling ayatollahs are afraid, I think of having the US in place on both major borders–in Afghanistan and in Iraq. They would be surrounded! And, Bush after all named them as part of an axis of evil and they have reason to be afraid that they are next on his hit list.
On the other hand, the expatriate Iraqi group, the Supreme Council for Islamic Revolution in Iraq, headed by the Hakim family, is hosted by Tehran and has been in close contact with the Pentagon about cooperating with an American attack. SCIRI has 10,000 troops in its al-Badr Brigade, which could come across from Iran into Iraq to support a US invasion. Although SCIRI has been criticized for these contacts by some ayatollahs, to my knowledge it has not been stopped from exploring them.
The idea of a Shi`ite-dominated Iraq, which is what would develop if Iraq had a parliamentary democracy (they are 60-65% of the population) must be appealing to Tehran.
So, I think they are of two minds about it.