Just guessing, because I haven't got a copy of the book, but I'd say this was a global variables problem. Gloabl; variables were disabled some time ago, with the release of PHP 4.1.0:
http://www.php.net/release_4_1_0.php (read the bit where it says "SECURITY: NEW INPUT MECHANISM"
Many books predate this change and contain examples which rely upon the assumption that global varaibles are available.
try
echo $_REQUEST['author'];
instead.