I meant to highlight this earlier in the week. But Dean Barnett has done a PHENOM job is contrasting the Sunni and Shia Muslim sects and the differences they hold.
After reading through this I began to understand why it is now so important in the minds of the the Saudis and other Sunni to get their hands on nukes - if Adolf-a-dinejhad has them - for self protection.
Bookmark Dean's post - you will find it handy at a future date I'm sure.