I have has some requests for more specific instruction on Live Preview, so here we go.  I will be as succinct as I can here, while still giving you all the information necessary to get this working.

First things first.  From now on the most recent versions of my plugins will be housed at wp-plugins.org, so go on over and grab the latest version .65RC1.  Okay your back now, good.

This newer version takes some of the complexity out of using the plugin, which I am sure you are all very happy about.  The plugin now handles inserting the needed javascript into your index.php file.  Okay so lets look at the steps necessary to get this all going.

Parts and Pieces

This tutorial will be written for 1.5 only so go away if you are not running the latest WordPress.  Follow these easy steps:

1. Upload the plugin to your WP install and activate it.
2. Open your comments.php template and find the following code around line 77: <textarea name="comment" id="comment" cols="100%" rows="10" tabindex="4"> And change it to look like this: <textarea name="comment" id="DynamicText" cols="100%" rows="10" tabindex="4" onkeyup="ReloadTextDiv();">
3. Then decide where you want the preview to show up, and when you have found that place add this function call: <?php comments_Div(); ?>

And that's all she wrote

And that is it people.  At this point when you save and upload your comments.php file to your live server you should have live preview.  If you don't then you did not follow these instructions exactly, or you have a conflict somewhere probably with another bit of javascript.