The commands i used:
sagi compizconfig-settings-manager // installs the compiz settings manager
ccsm // starts the settings manager
gconf-editor // starts the gnome configuration tool
In the compizconfig-settings-manager search the wallpaper plugin, add the 4 wallpapers you want and then activate it.Then start the gconf-editor and remove the check mark at apps>nautilus>preferences>show_desktop .
Your 4 workspace should now have different wallpapers.
If Unity displays the menubar or the dock incorrectly just log out and then log in again.

