If you see this message when you newly install OsCommerce
"Server Requirement Error: register_globals is disabled in your PHP configuration. This can be enabled in your php.ini configuration file or in the .htaccess file in your catalog directory."
then you need to create a php.ini file in the catalog directory with register_globals = On within it. This way you will turn globals on just for your site.
We turn register_globals off as it poses a security risk.