available editor problem

I got vs2008 professional edition on my computer and also installed msdn library,expression studio3,silverlight3 tools and toolkits. The problem is when i create a WpfApplication, in the Window1.xaml i cant see the design view. even i enter shift+F7(design view) it gives me an error "There is no editor available for 'C:\Users\Onur\Documents\Visual Studio 2008\Project\WpfApplication1\WpfApplication\Window1.xaml'. make sure the application for the file type (.xaml) is installed" vs2008 warns me in same manner for SilverlightApplications. Only with WindowsFormApplication i can see the design view. Please help. You can write here or send the solution to my e-mail [email protected].