WPF master detail binding

Ok, my first post, hope it's the right forum.

I need an example of a typical master detail scenario done in WPF (C#).
The ones I've found won't allow editing of the details.
I need a grid*containing one combo box for the master key value and a couple of editable combo boxes for detail values. I have observable collections for master and detail but I can't get it working. How should the bindings be set?

Thanks for any info,

Rainer Engblom