At present we host a number of WPF controls in a WinForms application. The application is started using the System.Windows.Forms.Application.Run(...)
If you host WPF controls within a WinForms application you do not have the Applicationobject which hosts the application-wide resources. The trick is to create such a object, load your global resources and merge them into the ResourceDictionary.
Here is an example of this code:
http://www.snippetsource.net/Snippet/26/load-application-level-resources-in-winforms-hosted-wpf-controls (Link fixed)