Just to add my 2p's to this topic and to hopefully help other newbies like myself...
I did what the OP said regarding renaming the 'admin' folder, so:
[Step 1] 'http://www.mysite.com/mycatalog/admin' --became-> 'http://www.mysite.com/mycatalog/newadminfolder'
(Needless to say the above site isn't real.)
Then:
[Step 2] changed 'newadminfolder/includes/configure.php' as per the OP's instructions
After Step 2, all attempts to access 'http://www.mysite.com/mycatalog/admin' should result in a 404 error, but I'll reach my osCommerce Administration login page at 'http://www.mysite.com/mycatalog/newadminfolder'
It's in the next step where I started scratching my head...good thing I found this handy tutorial, which also contains a neat tool (at the end of the tutorial) for generating your login and password for your would-be protected 'newadminfolder'
Here's the link:
http://www.addedbytes.com/apache/password-...-with-htaccess/ (Please read tutorial before continuing below)
[Step 3] Follow the tutorial for generating your .htaccess file and your login/password list for your 'newadminfolder'
[Step 3a] For the absolute path needed for the 'AuthUserFile' entry, I used the 'Backup Directory' entry found in 'Database Backup' tool inside osCommerce Administration
Example:
I created a new folder called 'mynewfolder' just outside of my catalog, so if my Backup Directory says '/this/is/where/you/are/mysite.com/mycatalog/newadminfolder/backups/' then I entered the following lines in my .htaccess file:
AuthName "My New Admin Page"
AuthType Basic
AuthUserFile /this/is/where/you/are/mysite.com/mynewfolder/.htpasswd
require valid-user
[Step 4] Upload the .htpasswd file under the 'mynewfolder' folder and
[Step 5] Upload the .htaccess file under the 'newadminfolder' folder
And that's it. The first time I go to 'http://www.mysite.com/mycatalog/newadminfolder' I get a pop-up window to enter a login ID/pswd, which should be found within my 'mynewfolder/.htpasswd' file, and if I get both ID/pswd correct then my osCommerce Administration login page gets displayed. I don't mind entering two login ID/pswd's.
Hope these help!