Separating designer from XAML window for WPF in VS2010

1. Open your XAML file as usual.
2. In the solution explorer, right-click on your XAML file and choose “Open with…”, then “Source Code (Text) Editor”, then OK.

You should now have two tabs for your XAML file, one in design view and one in code view. At this point, you can drag one of them onto your second monitor while leaving the other in place.

Hope it helps!