Gradient overlay

Hi,
I am uing the http://www.php-help.ro/examples/mootools_rotator/# script to use in a gallery however I am wanting to add a gradient layer on top of that so it appears to be slowly fading in.
so what I tred doing is creating the slide in the div and the drating a different div and setting that to a different z-index and adding a picture to it which is all fine and looks good however because it is above the gallery for some reason the images are not clickable but are when u get past the image. Would it be possible to get a image to sit ontop of a button using seperate div’s and still click the button and if so how could I do this?
thanx,
Daimz