Kant's Categorical Imperatives

[Mudhammam]

My question regards Immanuel Kant's "Categorical Imperatives." I haven't gotten around to reading Kant though he's definitely on my list of future endeavors, so my knowledge of him is limited to other's commentaries and a few Google searches. A few days ago I got into an unproductive argument with an apparently devout follower of Kant whose position it was, like Kant's, that if a murderer were to arrive at your doorstep seeking to slaughter your friend, whom you were harboring, it would be your duty NOT to lie to the murderer, even if the consequence was that your friend would end up getting massacred. I found this, well let's just say, INSANE! I didn't believe at first that that couldn't have actually been what Kant meant. But it appears that it was indeed an early objection to his moral philosophy and Kant never really came to see the problem with it. I'm coming to the issue from the position of, well let's call it "urbane consequentialism." What are your views on Kant in this example? From what I've read of Kant's contributions to the notions of "unalienable" "human rights" and "equality," I think he was on the right track in many ways...but failed to allow that every rule has an exception or two, even imperatives. The example of the murderer must be one of them. It must also be asked, how does a Kantian establish what is a "Categorical Imperative"? What about in the case of suicide?