How do you put a WPF control into a Windows Forms Form? Most likely I will be inserting my WPF control into a Windows.Forms.Panel.
Put an ElementHost control inside the panel. This control can then host a WPF element. From the WinForms designer, you can find this control under 'WPF Interoperability'. First you may need to add WindowsFormsIntegration.dll to your project's references.
For an example, see Walkthrough: Hosting a WPF Composite Control in Windows Forms.