Creating Help using HTML

I am in the process of authoring help per window on a 2000 window project using html.  As a result, I will have a total of about 2000 html files that can be accessed by one of two ways, either directly from the window the user needs help on or from a table of contents.  My problem is this:  I need to know the most efficient and logical way to create this table of contents.  I need to create in such a way that the user won't get lost in the table of contents.  The project is set up in a hierarchical tree structure.  There will be approximately six main trees, three of which will contain about 500 html files.  I need to be able to get from a help screen back to the the table of contents using a "Back to Table of Contents" button.  When the user gets back to the table of contents(TOC) I don't want them to feel lost by what they see.

Previously I was using TriTeal CDE help viewer which provided a means for creating a collapsible TOC but for this project it is not available to me.  All that I have to work with is an HTML 2.0 viewer in which frames is not available.  Any ideas on how to set up this TOC would be greatly appreciated.

                                   Thanks,

                                   Will Pincek