Thank you.
I suggest that the "Silverlight Designer for Visual Studio 2010" page needs to be brought up to date as it is no longer a tool just for Silverlight, and we are talking about VS 11 now.
There should be a link to the XAML designer in
"What's New in Visual Studio 11 Beta"
http://msdn.microsoft.com/en-us/library/bb386063(v=vs.110)
under:
Visual C++
Metro Style App Development Support
Native XAML-based UI model. For Metro style apps, you can use the new native XAML-based UI model.