Vista - Specify background picture location

Hi,

Is there anyone that can help me with the following?

I want to specify the desktop background picture location to a specific folder so that the user can select one of the images I've put there as their desktop background. I don't want them to be able to browse using the browse button and I only want my specified folder in the drop down (if the drop down can't be disabled completely). I don't want them to be able to select any other images as background with the "Set as background" option as well.

Is this possible?

I know I can specify one image as background using a GPO, but that will disable the option of changing the background all toghether and that's not what I want.

Thanks!