Hi, Heather, and welcome to the forums.
Actually, I feel like a dummy. WebHelp and FlashHelp don't
have a setting for plus/minus collapsers, so I almost said you
couldn't do it. Then I said, "Duh! Ask the Robowizard!"
You can get the same effect as collapsers by using custom
icons for your open and closed books. The "Open" book has the minus
box, the "Closed" book has the plus box. You don't get the lines,
but you get the behavior.
The icons are available on the Robowizard's web site:
www.robowizard.com > Grimoires > Books with Plus/Minus Signs.
The instructions on using custom TOC icons are in RoboHelp's help.
Good luck!
Elisa