Customize the Drupal 6 Comment Form
Originally I found this site that said this could be done within the theme, but I ended up going for a hook_form_alter.
http://pastebin.com/DJ47XUMy
// Put this in mymodule.module
/**
* Implementation of hook_form_alter().
*/
function mymodule_form_alter(&$form, $form_state, $form_id) {
switch ($form_id) {
case 'comment_form':
// Rename some of the form element labels.
$form['name']['#title'] = t('Name');
$form['homepage']['#title'] = t('Website (optional)');
// Add some help text to the homepage field.
$form['homepage']['#description'] = t('If you have your own website, enter its address here and we will link to it for you. (please include http://).');
$form['homepage']['#description'] .= '<br/>' . t('eg. http://www.mysite.com');
// Remove the preview button
$form['preview'] = NULL;
break;
}
}