As an Islamic theology, Iran has a very particular political system, which can be split in 2 parts to simplify it: the “normal” democratic branch with elected presidency (now Ahmadinejad) and parliament; and the Guardian Council. The Guardian Council is ruled by is Supreme Leader –Khamenei since 23 years– who is the real dictator in Iran: he is the highest state authority, he approves or not the members of the council who afterwards vote for him. The council validates the candidates for the presidency, accepting or refusing them. After some disagreement with Ahmadinejad, the council might be even more careful in his validation for the next presidency in 2013!
The 2nd branch has also his own security system, police (republican guard) and fanatics. It has something similar to the German Nazi time, SS versus SA, with the republican guards matching the SS.
The roles are however different: if the 1st branch is about the country and its laws, e.g. the police and the army protect the population in case of issue or war, the 2nd branch deals only with the system, ensuring its maintenance. If someone criticizes the system, he might have serious issues with those people dedicated to the system. And they are many: through the religion (mosque) “in the name of Allah”, in each city or village, the <> inform the police about possible crime done by “normal” people.
A religious dictatorship is maybe the most dangerous: as everything said by the leader is like said by God, the masses believe and support him.
With such a constitution, it is very difficult to see how the politics will change in the near future! Some say the council does not care much about the citizen but more about having a strong Islamic framework.