Animation question: rain?

A long time ago, someone posted (here, I think) a tutorial of how to do that "animated rain" effect on an icon. Now, as luck would have it, I can't find the tut (and in case you've been in a cave for a while now, the memories aren't working). Right now I only have Adobe Photoshop 7.0 and Imageready...is this possible? If not, is there a free program that I can get for it, and, more importantly, is there a tutorial somewhere that I can follow?