Added IIS 4.0 hints from Martijn Pieters and untabbified.

doc/WEBSERVER.txt

@@ -265,6 +265,32 @@ Zope authentication with existing web servers
 
       * An ISAPI module to support PCGI is under development.
 
+      * IIS 4.0 throws away Zope's error messages by default. This behavior
+      can create quite a few problems, including authentication problems.
+
+      Microsoft prides itself on the clear error messages that IIS 4.0 presents,
+      when the user makes a mistake. These error messages are implemented in the
+      form of Custom Error handlers, that return a file, or URL to a user when a
+      certain error occurs.
+
+      This means, that when you forget to fill in an Id when you want to create,
+      say, a new SQL Method, Zope's clear error message is replaced by IIS's
+      totally irrelevant error message. Also, it completely breaks authentication
+      when the user uses IE5.0 when trying to log into a secure area of the
+      server. These Custom Error handlers are enabled by default.
+
+      Luckily, the handlers can quite easily be switched off:
+
+      Open the IIS website in the Management Console, and navigate to the folder
+      you put the PCGI executable in. If you named your Zope installation 'Zope',
+      it will be called 'Zope.exe'. Double-click on that file. A property page
+      will appear. Select the 'Custom Errors' tab. Now, select every HTTP Error
+      code in the listbox that doesn't have type 'Default', and click on the 'Set
+      to Default' button for each one. This will disable IIS overriding the error
+      message returned by Zope.
+
+      Click OK, and voila, Zope is allowed to tell the world what it thinks went
+      wrong.