You can embed chatbox wherever you want on your site .
Example : on the top of your site
  1. Install the Simple Machines Forum to your website
  2. Get embed code chatbox
  3. Create function embedChatWing with width:100% heigh(option) file "Themes\default\index.template.php"
  4. Find function template_body_above file "Themes\default\index.template.php" and use function embedChatWing()
  5. Result