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