Hey Pete, no problem.
Basically in some, but not all, photochop applications (I have only knowledge of Photoshop CS2) you can add adjustments to your image (such as saturation and levels) as a separate layer. It allows you to chop and change them without affecting your original picture.
Now, each of these layers can have a mask associated with it which affects how much they apply to the resultant image. So, by default the levels adjustment applies equally to the whole image. If you modify the mask so that it applies fully at the top and gradually fades to the bottom you will have a graduated mask.
HTH
