There is a Visual Studio add-on that can help. However, it was not updated. It also helps you write code. To compile and run the code, you still need MonoTouch and Mac. https://github.com/follesoe/VSMonoTouch
Update: As of February 2013, Xamarin includes Visual Studio support for developing iOS applications in its Xamarin.iOS business class. You can fully get used to Windows + Visual Studio, but you still need a Mac on your network to build and run the simulator.
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