You can do this without installing additional software. Simply use
gconftool with a little shell script trickery (untested):
while [ 1 ]
find /path/to/wallpapers/folder -type f > ~/walls.txt
count=$(cat ~/walls.txt | wc -l)
for files in $(seq $count)
file=$(cat ~/walls.txt | head -n $files | tail -n 1)
gconftool-2 --type string --set /desktop/gnome/background/picture_filename "$file"
sleep 300 # wait 5 minutes before changing again
you'll need to change the
/path/to/wallpaper/folder accordingly. This will go through every image in the folder, changing every 5 minutes. Once they've all been used it will start at the beginning again, and regenerate the file containing the names of the wallpapers to include any new wallpapers.