Modifying the RSS feed(s)?

hi all ...

I have a requirement to use only one forums RSS feed [rather than all of them collectively], so I can post this to our news.

I have seen many ways in which to do this, from a newsletter Mod [which I think Rickard wrote], to others, and even a nifty Mod that Alex King wrote which essentially replaces the stock RSS feed(s) which ship with PunBB out of the box.

Essentially, I have a php script which pulls RSS feeds, and splits, creates the stories for me, and post those as close entries in my weblog.

The issue I have now is that I only require one forum, and not all of them.  So, my question is, can anyone tell me how to hack the existing RSS so that I can create a new feed, separate from our regular feeds, and use it instead?  This php file would be hidden, and used exclusively for our own use.

I hope this makes sense. 

All help appreciated.