I found the same problem working under w2k.  I found an answer querying the
global variable HTTP_GET_VARS and you can also query HTTP_POST_VARS (depends
if you are using GET or POST in your <form> statement.

I had a similar problem where my querystring function worked and isset()
showed that my variable wasn't set.
Good luck

function querystring($cString) {
// check with the get variables for a specific value
  global $HTTP_GET_VARS;

  $cRetVal="";
  while(list ($key, $val) = each($HTTP_GET_VARS)){
   if ($key==$cString) $cRetVal=$val;
  }
echo "querystring $cString=" . $cRetVal . "<BR>";
  return $cRetVal;
}