Trying to use the C# SpellCheck class

I am trying to use the SpellCheck class C# provides (in PresentationFramework.dll). But, I am experiencing problems when trying to bind the spelling to my textbox:

SpellCheck.SetIsEnabled(txtWhatever, true);

The problem is that my txtWhatever is of type System.Windows.Forms and the parameter this function is looking for is System.Windows.Controls, and simple converting failed. I also tried to make my TextBox of this type, but... couldn't. Does anyone know how to use this SpellCheck object? (MSDN wasn't that helpful...)

Thanks