php ALLWAYS makes the global arrays $_GET, $_POST, $_COOKIE, $_SERVER etc., allthough they can be empty because there simply isn't a variable to put in there for php
the setting register_globals is only to make those variable accesable as "normal variables" in you're scope so you can use $username instead of $_POST['username']
the setting "register_globals" has no effect on the super globals
Greetz Daan