Kubuntu, random background image at startup

[stan]

I'm building a machine that I plan on transitioning my wife to as a
workstation. She is curently using an older Debian machine, running an old
version of Gnome (1.4 if I recall corectly).

I have a small perl script that selects a random image from a given
directory, and makes this her background when she logs in.

How can I acomplish this same goal in the KDE version shiped with Kubuntu
6.10?
-- 
Unix is very simple, but it takes a genius to understand the simplicity.
(Dennis Ritchie)