I have a simple c++ windows form in visual studio 2010. I want to know if is possible to have this form working with chrome native client PNaCl.
No, Native Client plugins work on the Web Platform, which is inherently platform independent. That means no Windows, OS/X or other platform APIs are exposed.
You must either port your app to use HTML / CSS / Javascript + Native Client, or use Native Messaging to allow your web app to communicate with a Native App that contains your Windows Form.