Returned to the task of altering the Gnome desktop background. Sorted the issue out at last! As the Developer docs are pretty minimal in this area (consisting of nothing other than a list of function prototypes) I downloaded the Gnome desktop code itself and took a rummage through its dirty linen! What I found was that the calls to set the background etc, in fact modify the gconf settings. Ok, I can now get the background to change but, I don't want the delay of waiting for some Daemon to pick it up! At the moment it takes about 3-5 seconds for a background to change. Looking through the nodes for background slide shows, there appears to be some way of setting the transition duration. So, I'll follow this one up soon.