Here's a FRONTLINE interview with COL Macgregor where he clarifies a bit the scenario he was looking at for OIF I. I remember in Cobra II that he was ID'd as one of the main inspirations for Rumsfeld's concept of going in light. Specifically he said that it would only take 50k troops to knock over Saddam and that going in with over 120k was needless overkill.

In the interview he specifically advocates shooting straight through to Baghdad as fast as possible to topple the regime. He emphasizes that the IA would not fight, and that it was of paramount importance to get reconstituted Iraqi Army and police back into action as soon as possible for internal security. Essentially a decapitation strategy, but holding the rest of the regime, or at least its security forces, in place.