Ja... Der er en lille fejl.
<?
mysql_connect ("localhost","usr","pass");
mysql_select_db ("database");
mysql_query ("INSERT INTO guestbook (id,navn,emne,mail,besked)
VALUES ('','$navn','$emne','$mail','$besked'");
?>
Skal laves om til:
<?
mysql_connect ("localhost","usr","pass");
mysql_select_db ("database");
mysql_query ("INSERT INTO guestbook (id,navn,emne,mail,besked)
VALUES ('','$navn','$emne','$mail','$besked')");
?>
Dvs. du manglede lige en lille bitte ")".