Register_globals determines whether incoming get/post name/value pairs are turned into script variables. IE: if your form passes a form field "myFormField" with the value of "42", then your script will automatically have a variable "$myFormField" with the value of "42".
Put PHP_INFO(); into a test script and run it. It will produce output with all of the configuration options for your version of PHP. Look for "Register_Globals" and see if it is "on" or "off".
This may or may not be the problem with your script, but is as good a guess as any given the information you posted.