Under Visual Studio 2010 Professional, this keyboard shortcut goes by the name Window.PreviousDocumentWindow and Window.NextDocumentWindow.
Important Note: By default, Ctrl-PgUp and Ctrl-PgDown are assigned to Edit.ViewTop and Edit.ViewBottom respectively, so make sure to remove the existing keyboard assignment before trying out your new assignment. If you don't, the keyboard commands you enter will continue to be interpreted as the most "specific" shortcut (Edit.ViewTop or Edit.ViewBottom) since you're most likely trying this out in the Edit view!
