Well it's rather simple (but requires some graphics work on your part).

The unlock screen is part of the theme and contains the background for the sliding part (the "ball" that slides is not part of the image). Since I'm using the default theme, the image is located in /usr/share/themes/alpha/backgrounds/lockslider.png

(I've attached it as well)

I just used it as a template to GIMP a slider background on it on the correct spot and then overwrote the default theme image with mine:

(do this as root)
And that's about it.


(here's my panoramic desktop and the lockslider image for reference: abandoned.tar.gz)