How can I host a Windows Forms Composite Control in Windows Presentation Foundation ?

You can choose to keep your Windows Forms application primarily intact and migrate portions of your application to WPF where it makes sense. You can do this by identifying those areas of your application that are a good fit for WPF features and convert only those areas to WPF. For example, you may want to convert only a few of your forms to WPF and keep the rest of the application based on Windows Forms. Using this method, you could simply popup instances of WPF pages or windows from your Windows Forms application. Additionally, you may want to actually swap-out Windows Forms controls for WPF controls on a form resulting in a hybrid form when the controls co-exist in peaceful harmony.