Anyone tempted to support the move to teach Intelligent Design as a scientific theory of similar stature to evolutionary theory ought to begin by reading The Blind Watchmaker by Richard Dawkins. Interestingly it's subtitled "Why the Evidence of Evolution Reveals a Universe Without Design".
The argument against Intelligent Design is not all that difficult. In fact it's simple: it doesn't explain anything. To answer the question "where does the complexity of nature come from?" with "from pre-existing complexity (in the form of a creator)" is to provide no answer at all, because it brings you back to the same question - "well where did that complexity come from?"
As Dawkins explains so eloquently, evolutionary theory explains how complexity requires only simplicity, randomness and time to evolve. And the test of evolutionary theory is simply this: it explains the observable facts. Not perfectly, but that is why open minded and skeptical scientific enquiry continues to drive refinement in the theory. That's how science works.
Intelligent Design deserves the same status in the teaching of science as Lamarckism; as a discredited theory which very superficially makes sense but actually fails to explain any of the great body of evidence that is explained by evolutionary theory.