How to override node-xxx-edit.tpl.php in drupal 6

Could not find a proper solution yet. But, the temporary one goes here:

function custom_nodeapi(&$node, $op, $a3 = null, $a4 = null) {
switch ($op) {
case 'load':
break;
case 'prepare':
if ( arg(2) == 'edit' ) {
$form = theme('article_edit', $node);
}
break;
}
}

 In template.php 
function theme_article_edit($form) {
return _phptemplate_callback('article_edit', array('user' => $user, 'form' => $form));
}