What's in it for Iran? I'm speaking of the assertion that Iran is backing and encouraging the insurrection in Iraq. Since the Shiites dominate the Iraqi government and are sympatric to Iran, why would the Iranians want to create a civil war. They would be better off looking to stabilize Irag with a Shiite government in place. Therefore, I question the US-UK claims that Iran is behind the insurrection. While Iran might want to provide arms to some Shiite militias, I see no reason for them to want chaos in Iraq. Once the US is gone the Shiites can completely overtake the government and Iran will be in a more powerful position than ever.
I strikes me that a better approach for Iran in Iraq is to work to reduce the violence and do all they can to get the US to greatly reduce or remove it's troops. Once the US is gone, the Shiites with their Iranian backers could move with a free hand against the Sunnis and Kurds. This also reduces the number of US troops on their border. Reducing the violence seems to have more advantages then disadvantages for Iran.
This is a separate issue from the nuclear one. However, it could be the Bush administration is using the claim to bolster it's efforts to isolate or attack Iran.
I'm interested in hearing any thoughts on why Iran would want civil strife in Iraq. Seems counterproductive to me.