If Drupal is reporting register_globals is on, and you are not running a customized PHP, this is an indication that your domain is running PHP4 (which you can confirm, of course, with phpinfo() ), so your fix, in this case, is really easy:
Just go to "Domains -> Manage Domains", and click the "edit" button under the "Web Hosting" column for the domain.
On the next page, use the pull-down selection box to change your PHP to PHP5, and save the settings. That problem will be solved as PHP5 ships, by default, with register_globals = OFF.
Of course, this is a "one way" trip so be careful (more info here)! If you are running any software (osCommerce comes immediately to mind) that requires PHP4, you will only have made matters worse.
--DreamHost Tech Support