Using CakePHP all your form fields are normally populated automatically, it is easy to forget that to access the POST array all you need to do is use either:
$this->data or $this->params['data']
pr(); on either of these will present you with something like:
Array
(
[Book] => Array
(
[id] => 402
[name] => Everything about Everything
[publisher] =>
[ISBN] =>
[publish_date] => 15/04/2001
[summary] =>
)
)

