Homepage photos

I know I’ve seen a tut on this site that explains how to set up something that will randomly load different pictures from outside the page. OK, that wasn’t very clear. Here’s what I’m after,

On that page, I would like to have a different picture pop up everytime you visit the page. So I would have a folder with a bunch of pics on the server and the page would grab a different one randomly.

Any ideas.

The page is just html right now, but I’ll be doing the pictures in flash.