You get it here

http://www.ulead.com/download/freedownload.htm

It is Ulead Particle plugin. While you are there, Ulead Art Texture plugin and Ulead Fantasy Warp are well worth having too. They allow you to use some of the excellent features of PhotoImpact in programs like PSP and Photoshop that don't have anything like them built in. I spend hours just playing with the Art Texture one, just making patterns and so on for backgrounds, page borders etc. The particle one gives you rain, bubbles (raindrops if you make them small enough), snow, fireflies and a few other things of that sort that you might want to scatter around an image. Play with the various parameters to see what they do, because the effects can be very different when you change them. And every individual snowflake, bubble etc. can be moved around the image when you are making your snow or whatever, if too many are in one place. Just click on one in the preview in the plugin, and drag it to where you want it.

The fantasy warp is quite fun too. It is a bit like a kaleidoscope, but more variable, and you can pile the effects on top of one another to get different effects from using them singly.