The xxxxxx value will be held in the $_GET array provided to insert.php, so just use
$insVal = $_GET[insert_text];
then something like :
mysql_query("UPDATE tablename SET fieldname = '$insVal' where nws_id = 2");
But, be warned, you could be opening yourself up to sql injection attacks if you do not validate the insert_text value before. Do a search for htmlentities on php.net.
This should get you started anywayz.
Jeff