I'm currently creating an AJAX shoutbox using JavaScript and PHP. I was wondering what's the best way to build it.

I was thinking of storing a last shout ID in JavaScript and use it in the AJAX request to the PHP file:

shoutbox.php?last=21

If it is the last message then the PHP file would output nothing.
Otherwise if there were 23 shouts stored on the server for example, it would output the following XML:

xml Code:
<newshouts>
  <shout>
    <author>Bob</author>
    <message>Hello.</message>
  </shout>
  <shout>
    <author>Steve</author>
    <message>Sup.</message>
  </shout>
</newshouts>


Then in the JavaScript I would need to retrieve this data and add it to the shoutbox.
I would also need to remove the oldest two messages in the shoutbox because I want a certain number of shouts in the shoutbox at once.

Is this a good way to do it or is there a better/more efficient way of doing it?

If this is a good way I would like some help on writing the JavaScript code for it, especially removing the old messages from the shoutbox after adding new ones.

Thanks so much for you help.