Install webmin on ubuntu

download deb package of webmin from http://www.webmin.com/

sudo apt-get install libnet-ssleay-perl libauthen-pam-perl libio-pty-perl libmd5-perl
sudo dpkg --install webmin_1.330_all.deb

change gnome background by script

you can use this

gconftool-2 -t str --set /desktop/gnome/background/picture_filename "path/to/file"