I use 2 displays - laptop's built-in 1024x768 panel and external attached 1600x1200 CRT. In XFCE I could set different backdrops to these 2. Can I in Gnome?
It is not currently possible to do this with the default GNOME setup (ie. Nautilus, the file manager, manages the desktop wallpaper). There is an idea in development to provide this functionality. It is possible to use other software, such as compiz, to manage the wallpaper but I think this removes other desktop functionality (eg. files/folders/shortcuts on the desktop).