DOCBOOK-APPS: Section numbering depth

A friend and are are writing a book using DocBook V4.1 and our
publisher just told us that they would prefer section numbering only
be three levels deep.  In other words:

"Book Title"

   Chapter 1              <chapter>
     Section 1.1            <sect1>
     Section 1.2            <sect1>
       SubSection 1.2.1       <sect2>
         SubSubSection           <sect3> </sect3>
         SubSubSection           <sect3> </sect3>
         SubSubSection           <sect3> </sect3>
         ...

   We need it so the SubSubSections aren't numbered ( <sect3> and
below I suppose).

   We're currently using jade and DSSSL currently to render
PS/HTML/whatever ... what is the path of least resistance to modify
how sections are numbered in the chapters and TOC?  Do we need to
switch to DockBookXML + XSL?  Is there a parameter I can play with?
Help!  I have no idea..

   Sorry if this not a new question. Tried finding similar questions
in the list archives and couldn't.  Appreciate any help greatly!!  I
am only an Egg.

thanks in advance,

Greg Gallagher