I installed wp8 sdk. I've never use It yet but It seems to be working. When I try to launch the emulator I see only wp7 emulator and not wp8. Why?
Ok I solve the problem. I downloaded again and installed the SDK. I got a compatibility issue, but this time I could see all wp emulators. The problem was that my copy of windows 8.1 was not updated and for the SDK I was still using dev preview of windows 8.1. I updated windows and the sdk, and now all works fine :)