Now that interest in WPF is really heating up, we've been getting more inquiries about WinForms and WPF interop. Fortunately, we have a lot of coverage in the SDK docs, which shipped in November:

Migration and Interoperability

 

  • How to: Enable Visual Styles in a Hybrid Application
  • How to: Host a Windows Presentation Foundation Control in Windows Forms by Using ElementHost
  • Layout Considerations for the WindowsFormsHost Element
  • Supported Scenarios in Windows Presentation Foundation and Windows Forms Interoperation
  • Troubleshooting Hybrid Applications
  • Walkthrough: Arranging Windows Forms Controls in Windows Presentation Foundation
  • Walkthrough: Binding to Data in Hybrid Applications
  • Walkthrough: Hosting a Windows Forms Composite Control in Windows Presentation Foundation
  • Walkthrough: Hosting a Windows Forms Control in Windows Presentation Foundation
  • Walkthrough: Hosting a Windows Forms Control in Windows Presentation Foundation by Using XAML
  • Walkthrough: Hosting a Windows Presentation Foundation Composite Control in Windows Forms
  • Walkthrough: Hosting a Windows Presentation Foundation Control in Windows Forms
  • Walkthrough: Hosting an ActiveX Control in Windows Presentation Foundation
  • Walkthrough: Hosting an ActiveX Control in Windows Presentation Foundation by Using XAML
  • Walkthrough: Localizing a Hybrid Application
  • Walkthrough: Manually Adding a Windows Presentation Foundation Element to a Windows Forms Project
  • Walkthrough: Manually Creating a Windows Presentation Foundation Project Using Visual Studio
  • Walkthrough: Mapping Properties Using the ElementHost Control
  • Walkthrough: Mapping Properties Using the WindowsFormsHost Element
  • Windows Forms and WPF Interoperability Input Architecture
  • Windows Forms and WPF Property Mapping
  • Windows Forms Controls and Equivalent WPF Controls

Also, we have lots of sample code:

  • Arranging Windows Forms Controls in Windows Presentation Foundation Sample
  • Data Binding in Hybrid Applications Sample
  • Hosting a Windows Forms Composite Control in Windows Presentation Foundation Sample
  • Manually Creating a Windows Presentation Foundation Project Sample
  • Hosting a Windows Presentation Foundation Composite Control in Windows Forms Sample
  • Localizing a Hybrid Application Sample
  • Hosting a Windows Forms Control in Windows Presentation Foundation Sample
  • Enabling Visual Styles in a Hybrid Application Sample
  • Hosting a Windows Forms Control in Windows Presentation Foundation by Using XAML Sample
  • Hosting a Simple Windows Presentation Foundation Control in Windows Forms Sample
  • Hosting an ActiveX Control in Windows Presentation Foundation by Using XAML Sample
  • Hosting an ActiveX Control in Windows Presentation Foundation Sample
  • Mapping Properties Using the WindowsFormsHost Element Sample
  • Mapping Properties Using the ElementHost Control Sample

We have some designer-oriented topics as well, which shipped in Orcas Beta 1. These haven't been published at MSDN yet: 

  • How to: Copy and Paste an ElementHost Control at Design Time
  • Using Windows Presentation Foundation Controls
  • Walkthrough: Arranging Windows Presentation Foundation Content on Windows Forms at Design Time
  • Walkthrough: Assigning Windows Presentation Foundation Content on Windows Forms at Design Time
  • Walkthrough: Changing Properties of a Hosted Windows Presentation Foundation Element at Design Time
  • Walkthrough: Copying and Pasting an ElementHost Control into Separate Windows Forms
  • Walkthrough: Creating New Windows Presentation Foundation Content on Windows Forms at Design Time
  • Walkthrough: Styling Windows Presentation Foundation Content

Hope you can use them to build some neat hybrid apps.