Thanks for the code! I haven't ever played around with Javascript before but I know HTML, some CSS, and some basic PHP. Hopefully I can figure this out. It'll be interesting to see if it's possible to integrate it into WordPress though...that's what my site is in (http://www.fashion-shots.com).

I don't know javascript either. just used the script and with common sense, made it work.

I also want to use it when I re-create my website using wordpress. so let me know if it works.

I don't see why it wouldn't but we never know until we test

You're right - I'll let you know!

If it is for a website, i found this effect whilst browsing through free Javascript scripts.

http://www.rob-maxwell.com/retouch.htm

In Google (or other search Engine) type something like "Before/After Picture Javascript"

Yep I know it but I prefer the one I use because it follows the mouse.

But it's a good other possibility