Zipp Shimano or Campy dilema

Gentleman,
I don't mean to sound stupid, but I have not taken a new wheelset apart yet and I think I could use some input here. When I go on Ebay, ZIPP wheelset are set up as Shimano, or Campy. I would think that even if I buy a Shimano setup, It should not be too hard to change it to Campy cassette, or am I wrong? Am I going have to dismantle the whole wheel? Also, if I don't want either of them, Campy or Shimano, but I want to go with SRAM group, I wonder, what hub fits the SRAM? And final question: do I even have to swap the cassete from Shimano to Campy or SRAM if I wanna go to Campy or SRAM and why-the gears won't change properly? Thanks for your answers.