Edit the properties of your Microsoft HTML Help layout. Click
the Edit... button to the right of the "Advanced Settings". Click
the TOC Styles tab and make the following changes:
* Enable the Always Show Selection
Dismiss the dialog and open the Project Setup pod. Edit the
Window properties for the .CHM. Note that you may actually need to
define a window. If you see a window icon with a globe in it,
that's a WebHelp window definition.
So you edit the Window properties and ensure the
"Auto-synchronize TOC" option is configured.
After that, simply compile the .CHM and ensure the window is
defined as the default!