Drupal theming node teaser

<?php
if ($teaser) {
    // node is being displayed as a teaser
    // Anything here will show up when the teaser of the post is viewed in your taxonomies or front page
} else {
    //all other cases
    //Anything here will show up when viewing your post at any other time, e.g. previews
}

function phptemplate_preprocess_node(&$vars) {
    $vars['template_files'][] = 'node-' . $vars['nid'];
}