Like what pizzaman did, create a .htaccess file under the directory where osCommerce is installed. Add it there.
And you need to make sure the htacess support has been turned on.
I can't seem to get into the directory where osCommerce is installed. I created it as a separate directory (ex. ralphcherman.com/shop) and the admin panel is not allowing me to access. Is there a way to get into this to create the .htaccess file from my cPanel FTP or something? Thanks for all your help, I really appreciate it.
See if there is a "shop" directory accessible through FTP, and upload .htaccess file there.
You can also try to change the .htaccess file under public_html/, it will affect all php scripts in your site though.