I take it that NIS involves a mounting plate that is attached to the ski without putting screws into drilled holes. So how does the NIS plate get onto the ski? Is the mounting plate already on the skis when I buy them? Should I make sure that I don't buy skis that are lacking this mounting plate?
You are correct, the NIS plate is bonded to the ski at the factory, and the binding clips onto the plate--if memory serves, NIS plates can be found on some/all models from the following vendors:
Peltonen (not available in the US)
If you're going to use an R4 binding you need a ski with the plate, if the ski is not so equipped, simply use the R3 binding.
If you use the Salomon system, you can still attach a profil or pilot binding by drilling into the NIS plate. According to the folks down at FinnSisu, this works very well.