However, I found a relatively simple work-around, though I'll preface that saying I have some basic experience working with PHP scripts.
Inside the /moodle directory is a file config-dist.php. It appears to be a generic configuration file, possibly from an older day. (The build I'm using is 1.6.5.)
Open that config-dist.php file in a text editor, and modify it by putting in the information pertaining to your own server, such as database name and password, and location of your folders.
(If you've gotten to the point where you're stuck on the /admin directory problem, then Moodle has already already auto-detected some of this basic information about your setup, such as the path to the server directory - for example, with a RedHat server it's /var/www/html, etc. If you need to view that stuff again, delete the cookies from your browser and re-load the Moodle install page.)
Once you put that stuff, plus the MySQL passwords etc., in the config-dist.php file, save it as config.php and upload.
After I did this, the rest of the setup ran, and I now have a working site. Hope this works for someone else, too!
Tim
P.S. And I even got to keep moodle/admin as the admin folder!
