In Windows 7, I recently tried to add an item to my right click context menu that would only appear when the Desktop was right clicked, but it appears whenever I right click in blank space in any folder in explorer, as well. How can I make this item only appear when right-clicking blank space on the Desktop?
I think you would need a registry hack in order to do this, from what I am aware of. Essentially when adding a context menu to the right click menu the setting is being stored in the registry. Here is an article by a Microsoft Valued Professional blog on managing the context menu and is probably your best bet for learning what you want to do since it goes in to deep depth of editing context menus. Look in the areas that he is suggesting for editing, then find a "Desktop" specific item and that is the registry entry you are going to want to edit.
And here is a How To Geek to do exactly what you want.