Have aven't tried this myself yet, so I can only really make a suggestion.
You should try the a4j:push component. The browser will periodically check/poll for new events on the server and if there are any perform relevant rerendering.
You can also try a4j:poll which also periodically checks/polls the server. The difference is that a4j:poll will always cause a rerendering. I've used this component and it is dead simple.
Thanks - I'll look at doing a4j:poll or a4j:push.