When is Torture Acceptable?

Last night's episode of Lost was even more thought-provoking that usual. In the episode Sayid tortured a man that was captured in the jungle (thinking he is one of the Others), and it made me question my own ideas about when it is and is not acceptable to use torture as an intelligence gathering technique. On one hand, the amount of torture is wholly dependent on the person being tortured. If he doesn't want to be tortured, he has the option of telling what he knows, and the torture should stop. On the other hand, if the person is innocent, then he has no information to tell, and he's probably going to get a severe beating. At the very minimum, I think you need to have some evidence that the guy is withholding, rather than mere suspicion.