Moving comments around in Drupal is not (yet) straightforward. There is an experimental module that aims at providing this type of funcitonality, but the maintainers strongly discourage you in using it on live sites. If you're a daredevil, just go ahead and play with the
comments table. You might ruin your comment structure though… unless you want to understand how Drupal manages comments. After reading this post you should be able to move comments without fear.
Apparently Drupal 6 is not yet PHP 5.3 compliant. I noticed this today while updating a Drupal couple modules. When I wanted to run update.php I got a nice white screen with tons of messages about the