Multiple WP blogs in one feed

Hey guys

I have 4 different WP installs on my site (www.ectes.net; all WP installs are the same version).

Each seperate wp-rss2.php file (or whatever its called) works well. In short, it works the way it should straight out of the zip file.

However, what Im after is a way to have it so that the feeds for each different blog are combined in one feed page.

Hopefully this is understandable.

Thanks for your help

–Ectes