Some interesting information on the clash of cultures in Iraq:
Cultural unfamiliarity can be bad for troop morale.
The use of sniffer-dogs on Muslim civilians, for instance, are a no-no. So is holding a woman under detention for refusing to be searched this way.
There may be three Iraqs, not one: tensions between the Sunnis (Baghdad), Kurds (Mosul) and Shi'ites (Basra) could hinder the establishment of any one authority over the entire country.
The Washington Post has a summary of who Iraq's Shiites are. As with the Kurds.