PROBLEM SOLVED! Yeah!   
      
While reading one of numerous posts, in God knows which forum, something prompted me to go back to the very beginning, all the way back.  That is, IIS Configuration. 
  
The laptop I am working with is a new Windows 7 Dell Laptop that has never had IIS activated before now.  Well, I followed Lee Sykes' videos on "How to install DNN to Windows 7."  Video 1 explains how to prepare the environment and turn on IIS 7 and it says that accepting the default settings turned on by Windows should be good enough.  BUT, in the case of this laptop at least, IT'S NOT.   
      
To be sure of this, I went back and turned off IIS, rebooted, and turned it back on, accepting the defaults turned on by Windows.  Under the setting Internet Information Services\World Wide Web Services\Application Development Features, nothing is turned on by default.  AT MINIMUM YOU NEED .NET Extensibility, ASP.NET, ISAPI Extensions, and ISAPI Filters turned on.  After turning these features on and rebooting, all DNN Sites that I was having a problem with before, now work.   
      
You will probably want to turn on Web Management Tools\IIS Management Console too, in order to administer your IIS Server.   
      
Thank God this nightmare is over.  Hope this helps someone else find their answer.   
      
   Elgin  :D