It is possible to do it without coding.

Set rendering to module type
Control Panel -> Themes and aspect -> Rendering mode -> Custom module.

Then module mod_jchat woudl appear.
And JChat woud appears as this module.
You need to turn this module on. But don't set this module position (set position to nothing).

Then you need to add free plugin Modules Anywhere
And put JChat directly to article by writing {loadmodule mod_jchat,My Chat} anywhere in the article text.

But if you want JChat not to scroll (with article text), put Chat into div container with position fixed to screen.