I agree with everything Thomas said...look, there are three types of interrogation techniques. One is basic interrogation, including straightforward questioning and verbal trickery. Subject to various obstacles imposed by law (some of which are reasonable), that's perfectly OK for use with any prisoner. One is torture - and while we can understand how torture gets rationalized in a crisis, we should never, ever legitimize it beforehand.
But I can't agree with the idea that there is no middle ground between the two, anymore than I can buy into the facile effort to say that all prisoners are POWs or criminal suspects. Fact is, there are unlawful combatants who operate outside all norms of international law, who commit war crimes as a matter of course, and it is incumbent upon us to make clear to all the world that such people open themselves to harsher treatment than do enemies who respect the ancient laws of war. To do less is to encourage them to see their disregard of such rules as costless, and our obedience to them as a weakness.
Coercive but non-torture techniques like waterboarding may not always be the most effective methods of interrogation; that's up to the questioners. But I do think that making it known that we are open to using such techniques on such combatants is a useful way of sending them a message that there are consequences for their acts. If there is one thing history teaches us about international rules of conduct, it's that the only ones that get respected are the ones that carry real penalties for their violation.