Open a project (.hhp) file, and then click Add/Modify Window Definitions.
Add/Modify Window Definitions
Adds or edits window definitions and the general appearance of the HTML Help Viewer.
Type a name of up to eight characters for the secondary window you are adding.
Click the General, Buttons, Position, Files, Navigation Pane, Styles and Extended Styles tabs to create the features you want for your secondary window.