Hello Roger,

I do not know of any application that will automatically construct user
documentation.  There are applications like NDoc that will help you document
your source code and I believe Visual Studio now has that functionality built
in.  I have not come across anything that will compile user documentation
automatically as user documentation usually is written separately from code.  
We use an Adobe (previously Macromedia) application called RoboHelp.  You
might want to take a look at it as we have been pretty happy with it for the
most part. http://www.adobe.com/products/robohelp/

Let me know if you have any questions.