Islam means Submission (to god, Allah, in particular).
Unfortunately, this has been perverted to Submission to Imams that interpret the Koran the way they want to, similar to some of the American Fundamentalists and the Bible.
There are a couple of flavors of Islam, the Sunni and the Shi'ite.
The Sunni believe something to the effect that the leadership of Islam doesn't necessarily have to follow Mohamed's bloodline.
The Shi'ite believe it must follow his bloodline. It's bad for them that the last known bloodline sort of run into a cave and was killed (no, not Bin Laden, either.)