Just thought that this might help understand, at least some aspects of the differences.
HISTORY - A dispute over succession after the Prophet Muhammad's death in 632 split the Muslim world into Sunni and Shiite branches. Shiites believe Ali, the prophet's son-in-law, was Muhammad's rightful heir to lead the new faith. Sunnis believe the succession went to Abu Bakr, the prophet's close associate. Both branches follow the same basic tenets, including acceptance of the Quran as sacred text and sharing nearly all traditions based on the life of Muhammad and companions. But important differences include commemorations of rival historical figures, and the Shiite practice of giving greater authority to top clerics to interpret the Quran and traditions.
Las Vegas SUN: A Look at the History of Shiite Islam
There is more to the conflict than Saddam being a Sunni and stompin' on the Shi'a.