rediff from from http://drupal.org/node/43145
diff -ur -w drupal-4.6.5/modules/comment.module drupal-4.6.5.comment/modules/comment.module
--- drupal-4.6.5/modules/comment.module	2005-11-15 22:37:56.000000000 +0200
+++ drupal-4.6.5.comment/modules/comment.module	2006-01-11 18:01:10.000000000 +0200
@@ -92,7 +92,7 @@
     $items[] = array('path' => 'admin/comment/edit', 'title' => t('edit comment'),
       'callback' => 'comment_admin_edit', 'access' => $access, 'type' => MENU_CALLBACK);
     $items[] = array('path' => 'admin/comment/delete', 'title' => t('delete comment'),
-      'callback' => 'comment_delete', 'access' => $access, 'type' => MENU_CALLBACK);
+      'callback' => 'comment_delete', 'access' => 1, 'type' => MENU_CALLBACK);
 
     // Tabs:
     $items[] = array('path' => 'admin/comment/list', 'title' => t('list'),
@@ -266,8 +266,13 @@
       break;
 
     case 'delete':
+      if(variable_get('comment_delete_mode', 0) == 1) {
+        db_query('UPDATE {comments} set status = 1 WHERE nid = %d', $node->nid);
+        db_query('DELETE FROM {node_comment_statistics} WHERE nid = %d', $node->nid);
+      } else {
       db_query('DELETE FROM {comments} WHERE nid = %d', $node->nid);
       db_query('DELETE FROM {node_comment_statistics} WHERE nid = %d', $node->nid);
+      }
       break;
 
     case 'update index':
@@ -320,6 +325,10 @@
   $group .= form_radios(t('Location of comment submission form'), 'comment_form_location', variable_get('comment_form_location', 0), array(t('Display on separate page'), t('Display below post or comments')));
   $output .= form_group(t('Comment posting settings'), $group);
 
+  $group = form_radios(t('Delete mode'), 'comment_delete_mode', variable_get('comment_delete_mode', 0), array(t('Delete'), t('Unpublish')));
+  $group .= form_radios(t('Node owner can delete node comments'), 'comment_moderating_nodeowner', variable_get('comment_moderating_nodeowner', 0), array(t('Disabled'), t('Enabled')));
+  $output .= form_group(t('Comment management settings'), $group);
+
   $result = db_query('SELECT fid, filter FROM {moderation_filters} ');
   while ($filter = db_fetch_object($result)) {
     $thresholds[$filter->fid] = ($filter->filter);
@@ -672,6 +681,7 @@
 
 function comment_links($comment, $return = 1) {
   global $user;
+  global $node_info;
 
   $links = array();
 
@@ -681,8 +691,15 @@
   }
 
   if (node_comment_mode($comment->nid) == 2) {
-    if (user_access('administer comments') && user_access('access administration pages')) {
+    if ($node_info['uid'] == $user->uid && variable_get('comment_moderating_nodeowner', 0) == 1 || user_access('administer comments') && user_access('access administration pages')) {
+      if (variable_get('comment_delete_mode', 0) == 1) {
+        $links[] = l(t('unpublish'), "admin/comment/delete/$comment->cid");
+      } else {
       $links[] = l(t('delete'), "admin/comment/delete/$comment->cid");
+      }
+    }
+
+    if (user_access('administer comments') && user_access('access administration pages')) {
       $links[] = l(t('edit'), "admin/comment/edit/$comment->cid");
       $links[] = l(t('reply'), "comment/reply/$comment->nid/$comment->cid");
     }
@@ -707,6 +724,12 @@
 function comment_render($node, $cid = 0) {
   global $user;
 
+  // Give out node owner information to detect node owner:
+  global $node_info;
+  $node_info = array();
+  $node_info['uid'] = $node->uid;
+  $node_info['nid'] = $node->nid;
+
   $mode = $_GET['mode'];
   $order = $_GET['order'];
   $threshold = $_GET['threshold'];
@@ -959,9 +982,18 @@
 
   $output = '';
 
+  // Access check
+  if (
+    user_access('administer comments')
+    || variable_get('comment_moderating_nodeowner', 0) == 1 // comment_moderating_nodeowner Enabled
+    && db_fetch_object(db_query('SELECT uid from {node} where nid = %d and uid = %d',$comment->nid,$GLOBALS['user']->uid)) // user owns node
+  ) {
+
   // We'll only delete if the user has confirmed the
   // deletion using the form in our else clause below.
+
   if ($comment->cid && $_POST['edit']['confirm']) {
+
     drupal_set_message(t('The comment and all its replies have been deleted.'));
 
     // Delete comment and its replies.
@@ -990,7 +1022,12 @@
     drupal_set_message(t('The comment no longer exists.'));
   }
 
+  } else {
+    drupal_set_message(t('You are not authorized to access this page.'));
+  }
+
   print theme('page', $output);
+
 }
 
 function comment_save($id, $edit) {
@@ -1609,8 +1646,13 @@
 
 function _comment_delete_thread($comment) {
   // Delete the comment:
+  if (variable_get('comment_delete_mode', 0) == 1) {
+    db_query('UPDATE {comments} set status = 1 WHERE cid = %d', $comment->cid);
+    watchdog('content', t('Comment: unpublished %subject.', array('%subject' => theme('placeholder', $comment->subject))));
+  } else {
   db_query('DELETE FROM {comments} WHERE cid = %d', $comment->cid);
   watchdog('content', t('Comment: deleted %subject.', array('%subject' => theme('placeholder', $comment->subject))));
+  }
 
   module_invoke_all('comment', 'delete', $comment);