Scaled and centered option shows background image in right 1/3rd of screen, left is default suse-green.
zoom option zooms in only on top-left 1/3rd of the background and displays it on the entire screen magnified. It does not zoom in on the whole picture and display it correctly.
I use Gnome on 126.96.36.199-0.1-default #1 SMP 2008-08-21 00:34:25 +0200 x86_64 x86_64 x86_64 GNU/Linux
PS: How can I attach screenshots and xorg.conf here?