Saddam is quite the secularist. Except for a bit of opportunism in throwing some cash at the families of suicide bombers, he isn't on the same side as Osama. Would, perhaps, be at war with him if it weren't for Israel and the US being better targets.
This stuff is way complicated.
The reason for gearing up for an attack on Iraq is not complicated: GWB is under the impression that 9/11 gives him permission to do anything military he wants as long as the sand-colored uniforms are worn. And that makes this a good chance to restore the family honor.