Cross Platform UI - Using WinForm for Windows and Cocoa for Mac

Hi,

I have a WinForm application which I want to port to MacOSX.

I want to write a different UI layers for Windows and Mac to supply a native user experience in each of the platforms.

I wrote my WinForm code using VS 2005.
Now I want to write the code for Mac using Cocoa Sharp.

I have some questions before I start:

1. Can I compile Cocoa code on Windows using VS2005?
2. How can I reference to the assembly of Cocoa Sharp from MonoDevelop?
3. What is the best workaround write two different UI layers using Mono.

Thanks in advance,
Yoav