Well, there is a LOT of info out there on kidney disease and diets, it depends on how bad the kidneys are I think. Whole Dog Journal did a whole series of articles on it, I have a few of them photocopied and could mail them to you if you can't find them anywhere else.
Do your research if you're branching out from the SD. Science Diet K/D isn't the best option for every dog, but with damaged kidneys, I know you wouldn't want to risk making anything worse.