SpaceSuit (http://www.docklandsoft.com/spacesuit/) makes it much easier to distinguish your Spaces in Leopard. Once installed, it allows you to set a different wallpaper for each Space. If you use Spaces, you'll be amazed at how much better it makes Spaces as it's so much easier to recognize a Space without thinking about it. Seems like something Apple should consider adding as a default feature in Spaces since it makes it so much more intuitive to use.