In Drupal 4.7 you have to go to : administrator > settings > posts>> . The default teaser is 600. You can adjust it to 200 – 2000.
To make the teasers to zero length you will have to update your node.tpl.php file & add a “if” block ( if page == 0 ). Here is the example snippet of one of the node.tpl.php. Make sure you modify your theme’s node.tpl.php