david is right, you can’t see the transparent flash in Netscape. So that could pose a problem. I don’t care much for Netscape, so my site has everything that works with IE, but I didn’t use codes that work in Netscape, so it doesn’t work for Netscape users. If you don’t mind only IE users being able to see your pages you can do the overlay in flash.
Attached I have written an HTML page that allows the overlay of Flash on HTML. I have never done it before, but I figured I would give it a whirl. Just download the .zip file and unzip all the files into the same folder. The .fla was made in Flash MX with suprabeeners code on random motion. There is a tutorial for it at www.kirupa.com, there is also a tutorial for Flash 5 random motion.
The .zip files includes the .fla, the .swf, the .html file and a readme.txt file which i recommend reading before you start.
If anyone else knows any other way to do this, I would be interested in how.
Hopefully this is what you wanted.