ReverseAjax newbie

Can someone shed some light on
dwr.engine.setActiveReverseAjax(true)

and on the pollAndCometEnabled parameter in web.xml

what goes where and maybe why as well.

I tried using ReverseAjax but unsuccessfully.

I have a jsp which creates an instance of my AjaxHandler java class which should
then update the webpage when ever it needs to with the WebContext. However, the
webContext instance is valid when I call AjaxHandler.callMe() from javascript
but when I try to use it to get a scriptSession it is null. :o(

I'm guessing that dwr.engine.setActiveReverseAjax(true) and the
pollAndCometEnabled parameter have something to do with this problem but again,
I started working with DWR two days ago :o(

Help, anyone?

THANKS!!!