It's in the strangest place in Drupal 5, but you're looking for the Post information setting in Site building > Themes > Global settings. Make sure the boxes next to your products are checked. If they already are, you need to dive into the node template of your theme. Look for a line like
<?php
if ($submitted):
?>The lines after that should deal with $node->created.
If you need to, you can steal some code from other themes. Here's Garland's in full:
<?php
if ($submitted):
?><?php
print t('!date — !username', array('!username' => theme('username', $node), '!date' => format_date($node->created)));
?><?php
endif;
?>
Joined: 08/07/2007