Rollover Pop-up Image

[icu222much]

I've been browsing around online for an image pop-up script similar to the one used by iStockPhoto ( http://www.istockphoto.com/file_sear...ce&action=file ). Does anyone know how to code something like this?

I basically am looking for something where when the mouse rolls over the image, a new image would appear over top the existing content. For each new image that is appearing, I would like to include a short description of each image. Also, my images will vary in dimensions (height & width). I have looked at a bunch of roll-overs but I could not find one where you can vary the height & width.