How can I display author name, picture and signature when viewing a full node in D6?
Figured it out. To add a $user_signature variable to your node.tpl.php file, add this function to your template.php file:

function YOURTHEME_preprocess_node(&amp;$vars, $hook) {

  $account = user_load($vars['uid']);
  $vars['user_signature'] = check_markup($account-&gt;signature, $account-&gt;signature_format);
}