Bin Laden's muj had to stay hidden in NE Kurdistan under the protection of our no-fly zone or they would have been killed. Ansar al Islam was largely Kurdish old school muj from Afghanistan and they absolutely hated Saddam for gassing the Kurds.
They would have mutinied from al Qaeda if they ever sniffed a connection between bin Laden and Saddam. Bin Laden and Zawahiri didn't need Saddam for anything. At the time they were operating freely in Afghanistan and Pakistan with many training camps, etc.
Bottom line, we needed Iraq for a weapons and intel platform for the coming Islamic civil war and al Qaeda offensive. The Joint Chiefs well knew that 10,000 trained terrorists were coming out of the al Qaeda camps and that we needed a garrison for the hell-a-comin'. We also needed an end strategy for the no-fly zone partitioning. We did the right thing for the right (strategic) reasons and the wrong (public) reasons.
That is, 10,000 terrorists a month, being trained. We should have attacked Afghanistan 2 years before 9/11.
With due respect, I've never bought the idea that Saddam and Osama were such ideological enemies, they could never cooperate on anything. It always struck me as the kind of leftist myth that the left used when they had no real argument, similar to "It's all about oil".