How do I configure external.php

[datarecall]

<a href="http://www.domain.com/forum/external.php?type=rss" target="_blank">http://www.domain.com/forum/external.php?type=rss</a>

how do I actually put in the description part of the post rather then :

<description>
Forum: Forum title
Posted By: Widow Maker
Post Time: 08-28-2006 at 07:34 AM
</description>

I would rather like <description>today I went and grabbed and then I .......</description>

Is there any way to do this ?