The only way I can think of to have a shoutbox or similar element update itself when somebody posts a new 'shout' and it needs to be loaded in everyone else's browsers is to have Javascript check every x seconds for any updates... This could get a bit resource intensive though I expect if many people were to leave their browsers open on the page, idling.

Is this the only way or am I missing something?

I've prefer to stick to only html, css, javascript (AJAX) and php.