There's no need to use both session_register and $SESSION...it's one or the other depending on how register_globals is set in your version of php. If register globals is turned on, use session_register. If it's turned off, use $SESSION instead. The better way is turn register_globals off and use $SESSION....
session_start();
$_SESSION["var"] = "data";
print $_SESSION["var"];
that should output "data".