Okay. I started over. I dropped all the tables from the database, then ran the createtable.php script. I then added two users, and one discussion board.
1. When I go to the "rename group" admin function, it does not list any groups in the pull-down menu. (which is correct - before I was getting the phantom "users" group here).
2. When I go to the "change user's group" option, only the "user" group is shown. The box is checked by default. I unselect it, then reselect it, then click "submit". After the change has been made (which is really "no change"), I go back and refesh that page. Even though I had the box selected when I clicked "submit", the group is now unselected, and there's no way to make the change back to selected hold.
3. When I go to "change a board's read groups", I have four groups to select from - admin/moderator/user/guest. This seems correct. But if I make and save any changes, all the boxes get turned off for that board - so noone is allowed access to it. :-)
4. Perhaps something related - I go into the private message and try to delete the "welcome" message by clicking the "delete" checkbox to the right. Clicking the "delete checked" button will refresh the page - but the message is still there, and the delete checkbox is again turned off. Maybe there's a connection between the problems and the checkboxes?