A campy cassette will need a Campy-specific body to sit on. For Mavic, and presumably some others, you can buy the same wheels(i.e hubs) with either Shimano or Campy bodies. This also lets you switch between campy and Shimano body on the same wheel.
But AFAIK there's no Shimano body that will take a Campy cassette. I think I've seen some 3rd party cassettes though which mix Campy sprocket pitch with Shimano body splines. Won't help you as you already have a cassette.