Developer Guide to Migration and Interoperability in "Longhorn": Chapter 5: Recommendations for Windows Forms and "Longhorn" (The Developer's Guide to Interoperability and Migration in "Longhorn"): "Choosing Between 'Avalon' and Windows Forms
In situations where an application can be built exclusively to run on 'Longhorn,' we encourage developers to rely on the 'Avalon' classes so that they can take full advantage of the platform's capabilities. Developers who must maintain a single code base for a Windows client application that can run either on earlier versions of Windows or on 'Longhorn' should build their UI using Windows Forms. They should structure their applications in such a way that the 'Avalon' UI-based features are available if the application is running on 'Longhorn.'
Developers can accomplish this by referencing these features in a DLL that is either loaded or not loaded, depending on the underlying operating system version. This way, users running earlier operating systems such as Windows XP can access the entire application through Windows Forms, while 'Longhorn' users can take advantage of the added features in 'Avalon.'"