Thanks Carlos, those are both great articles.  Your whole collection of
articles is very impressive.

The suggestions got me 90% of the way there.  When I get to the
ImageList's Images property descriptor, it's value is of type
System.Windows.Forms.Design.ImageListDesigner.  This must be private or
internal class because there's no way to declare a variable of that
type (I get an "inaccessible due to its protection level" error when
compiling).

So I've gotten to the property, I just can't get or set the value.
Here's my code:

// get the Windows Form designer
designerHost =
(System.ComponentModel.Design.IDesignerHost)designerHostObj;
// get the designer's control container
container = designerHost.Container;
// iterate over the components
foreach (IComponent component in container.Components)
{
   // check if we've got the image list
   if (component is ImageList)
   {
       PropertyDescriptorCollection pdc =
TypeDescriptor.GetProperties(component);
       PropertyDescriptor pd = pdc["Images"];
       string x = pd.GetValue(component).ToString();
   }
}

It finds the image list and at the end if the if block, x =
"System.Windows.Forms.Design.ImageListDesigner+OriginalImageCollection"

Any idea where to go from here?  Thanks again for the great help!