In case anyone is interested...
I ended up implementing the interface in C# and then used that implementation in PB. I was able to change the value of a property on the implementation class and see it reflected in the window through data binding of the text of a button.
I've posted the examples on my skydrive.
The C# implementation is called PropertyChangedAssembly.
The PB example is called TestNotifyPropertyChanged.
https://skydrive.live.com/?mkt=en-US#cid=D13D80A62EA55460&id=D13D80A62EA55460%21108
I know its a simple concept but I gotta start somewhere.
Mark