The answer

[Jive Dadson]

Okay, with your help I've figured it out.  Instructions are below, but 
read the caveat by Ben Fenny in this thread.  All this stuff is good for 
one default version of Python only.  The PYTHONPATH described below, for 
example, cannot specify a version number.  Yes, that's a pain in the 
butt, but there's no way around it.  If you switch versions, you may 
have to delete all the .pyc files that will show up in the module 
folders.  Python ought to check them to see if they are valid, but I do 
not know if it does so.

These instructions are for MS Windows.

1) Create your modules folder. Let's say it's named "Modules."  The 
documentation calls it a "package."

2) In an explorer window or on the desktop, right click on My Computer, 
and select Properties.

3) Select the Advanced tab, and click on Environment Variables near the 
bottom.

4) Look for an environment variable named PYTHONPATH.

    a) If you do not find one, create one using the New button(s). I 
don't know if it has to be in User Variables or System Variables.  To 
save time experimenting, I just put one in both. For the value, put the 
full path of the folder Modules.

    b) If there's already a PYTHONPATH,  Edit it, adding a semi-colon 
and the full path of folder Module to the end.

5) Put your module folders into the folder Module.

6) (Here's a really arcane bit.) Into each module folder, put a file 
named __init__.py.  It will be executed when you load the module.  It 
can be empty, but it has to be there or else the module folder will be 
ignored.