The Geneva convention on the treatment of prisoners of war would be a good place to start. Certainly it should be applied to prisoners that are taken when we go to war (eg. Afghanistan). A big problem with it may be that is somewhat out of date in reference to precice procedures relating to non-state based organisations (eg. Al-Qaeda) but I would imagine that it should not be beyond the wit of the legals to take the principles of the Geneva convention and apply them in the modern context.