Ed,
You need to edit the reference page for the TOC. Specifically, the line that generates the entry for chapters. It should already have the building block <$pagenum>, or something similar, in it. Before this building block, add the building block <$chapnum>, the a hyphen or whatever character you want to separate them. This last building block is a placeholder for the chapter number. Then update your book.
If the numbering does not start at one and continue properly, then you need to set the chapter numbering from the book file. Right-click each chapter and select Numbering. Set the first chapter to start at 1, and the other chapters to continue from previous. Update the book.
That should do it.
Note that if the OTHER entries in the TOC use the same line in the reference page, you will have to create different tags for those "chapters" so that they have their own lines on the reference page, without the chapnum building block.
Good luck,
Van