if you haven't already, perhaps you should familiarize yourself with the php manual.
http://www.php.net/manual/en/ref.session.php
session_register(), besides requiring 1 or more arguments of what you want to register (you have none), should not be used if you're using $_SESSION globals. you should use session_start().
"If register_globals is disabled, only members of the global associative array $SESSION can be registered as session variables. The restored session variables will only be available in the array $SESSION.
Use of $SESSION (or $HTTP_SESSION_VARS with PHP 4.0.6 or less) is recommended for improved security and code readablity. With $SESSION, there is no need to use the session_register(), session_unregister(), session_is_registered() functions.
"