The two Vista machines see each other's files. Tha was accomplished by using just the sharing dialogue boxes.
The two Win 7 machines see each other's files. That needed two steps: the standard networking diaogue box for sharing; putting one password on both machines "homegroup"
The Vista machines cannot access the Win 7 machines' files.
One Win 7 machine can see the files on both Vista machines.
One Win 7 machine can see the files on one Vista machine only.
Now, all the permissions are in place, all of the sharing options in Network and Sharing Center| Advanced sharing settings have been made identical.
Apparently, Homegroups are new with Win7 so one cannot even have one in Vista.
I have seen two threads across the internet: 1.) you will never get this done, it cannot happen; and 2.) easy as pie just do XXX [where XXX=the steps I have already taken] blah. blah, blah.
Anyone got any helpful hints?