Assume that you're developing a Windows Presentation Foundation (WPF)-based application that uses layered windows. In this situation, you set the Window.AllowsTransparency property to True. However, layered windows may be rendered incorrectly in a Windows XP environment when NetMeeting or other screen-sharing technologies are used to share the contents of the screen.
To work around this issue, don't use layered windows in WPF-based applications that are running in a Windows XP environment.
There are known compatibility issues with displaying layered windows over various remote display applications that are running in Windows XP. Therefore, we recommend that you avoid using layered windows in this situation and instead use an alternative approach, when one is available. For example, you can produce a similar window appearance by using the native SetWindowRgn function to create non-rectangular windows.
For more information about the SetWindowRgn function, go to the following Microsoft website: