You need to rename your admin directory. Once that is done you need to update the configure.php files to reflect the name change.
example: define('DIR_WS_ADMIN', '/admin/'); should be define('DIR_WS_ADMIN', '/newname/');
and
define('DIR_FS_ADMIN', '/home/content/n/d/e/username/html/admin/'); should be define('DIR_FS_ADMIN', '/home/content/n/d/e/username/html/newname/');
As far as the .htaccess file..... you can just copy the .htaccess file to your image directories. I just used the .htaccess file from the image directory of the latest oscommerce download.