Setup existing drupal 6 site on local server
Steps to setup a Drupal Site : 


Place your Drupal 6 directory in your htdocs directory of xampp folder. All files and design folder should be at same place where they are on live version of site.
Open your settings.php, change the database credentials according to your local server.
Restore your database using phpmyadmin.
May be some image would not be shown up on site so you need to setup a domain in apache's vhost file.