Robert Hall has put together a PHP script that will allow you to ping the Macromedia XML News Aggregator (MXNA) when your site / weblog has new content. By doing this, you content will get added to the aggregator immediately.
If you are using PHP and not using MovableType (which has support for pings built in), this could be very useful.
You can find more info on pinging MXNA here.
You can find more info on Robert’s PHP ping script here.