You aren't even reading my posts.
The underestimation was not of what Saddam would do. The underestimation was of how far his troops/Fedayeen would go, even to the point of killing their own civilians and soldiers.
And it may not have been that much of an underestimation...there is a large contingent of special forces performing covert operations in Iraq right now. They have been there since well before the battle, and are engaging Fedayeen with snipers and car bombs. There are things happening there that pale anything Hollywood could dream up.